Akimitsu Ishizawa

Development of the spinal nerves in the mouse with special reference to innervation of the axial musculature

Development of the mouse spinal nerves was studied. On E11 (11th day of gestation), the primitive spinal nerve fascicle extended ventrally in the anterior half of the sclerotome. Spinal nerves in the forelimb region united with each other to form the primitive brachial plexus. Their terminal segment was covered by a peculiar cell mass. On E12, five primary branches developed along the primitive spinal nerve trunk. The ramus dorsalis was originally a cutaneous nerve, supplying two series of branches to the skin of the back. The medial series was derived from the dorsal ramus of C2–C8, and the lateral series from C8 and the more caudal dorsal rami. Nerves of the former series took the presegmental course through the intermyotomic space, while those of the latter the postsegmental course. The ramus cutaneus lateralis was a nerve that took the presegmental course to become cutaneous. The ramus intercostalis externus was a muscle branch whose distribution was restricted within the segment. The ramus anterior was a muscle branch from the end of the primitive spinal nerve trunk. The ramus visceralis connected a thoracic nerve with the para-aortic sympathetic cell cord. On E13–16 the ramus anterior secondarily gave off a cutaneous branch (ramus cutaneus anterior). The ramus intercostalis externus extended ventrally deep to the intercostalis externus muscle, crossing just caudal to the ramus cutaneus lateralis that secondarily gave off branches to the obliquus externus abdominis muscle.

Fetal development of the transverse atlantis and alar ligaments at the craniovertebral junction.

Although the fetal development of the craniovertebral junction has long been of major interest to embryologists from the viewpoint of segmentation, development of the associated ligaments has received scant attention. Using semiserial horizontal sections from 18 embryos and fetuses (six embryos with a crown‐rump length (CRL) of 20–26 mm or ∼6–7 weeks of gestation; five fetuses with a CRL of 32–58 mm or 8–9 weeks; seven fetuses with a CRL of 90–115 mm or 14–15 weeks) without any abnormalities of cartilage configuration such as atlas assimilation, we studied the ligamentous structures along and around the odontoid process of the axis. The transverse atlantis and alar ligaments originated from a common mesenchymal condensation possibly corresponding to the proatlas segment: the former started to develop slightly earlier than the latter, and the morphologies of both were established at 7 weeks of gestation. Development of the joint cavitation around the odontoid process began in the mid‐anterior area at 6 weeks, but was not fully completed even at 15 weeks (115 mm CRL). The presumptive joint cavity expressed vimentin and CD34 and contained abundant CD68‐positive macrophages. We always found a mid‐anterior joint cavitation facing the basi‐occipital, but the embryological meaning remained unclear. The apical ligament appeared most likely to originate from the notochord sheath. The notochord was exposed from the tip of the odontoid process toward the loose epidural tissue and entered the occipital bone, but was difficult to trace to the anterior surface of the basi‐occipital. Clin. Anat. 25:714–721, 2012.

An electron microscopic study of autonomic nerve cells in the cloacal region of the lamprey, Lampetra japonica.

SummaryTwo types of autonomic nerve cell in the cloacal region of lamprey,Lampetra japonica have been studied by electron microscopy. Large ganglion cells (LGC) were unipolar and individually invested with a satellite cell sheath. The LGC-satellite cell complex measured 24 μm × 38 μm on average. Granular endoplasmic reticulum and cored vesicles (80–140 nm in diameter) were scattered in the perikaryon. Two kinds of peculiar cytoplasmic filament were seen in LGC: one type was about 20 nm in diameter with periodic dense material on the surface and the other had a diameter of about 8 nm and showed an undulating profile. Nerve endings containing abundant small clear vesicles (30–50 nm in diameter) and a few larger cored vesicles (50–100 nm in diameter) were found in synaptic contact with LGC. Small ganglion cells (SGC) were also unipolar and covered incompletely by a satellite cell sheath. The SGC-satellite cell complex measured 6 and 12 μm on average. The SGC was packed with organelles and the perikaryon appeared more electron dense than that of LGC. SGC perikaryonal cytoplasm contained dispersed granular endoplasmic reticulum and numerous large cored vesicles (55–220 nm in diameter). Nerve endings containing numerous large cored vesicles (70–170 nm in diameter) and variable numbers of small clear vesicles (30–50 nm in diameter) were seen on the surface of SGC.

Intersection patterns of human coronary veins and arteries.

Intersections between the coronary veins (CV) and arteries (CA) of 103 adult human hearts were mapped on the heart surface. Then the correlations of these intersection patterns to their localization were studied. Eight spots were selected where one of four major CV (anterior cardiac vein, middle cardiac vein, left posterior ventricular vein, and great cardiac vein) intersected with one of CA and their branches (right coronary artery, posterior interventricular branch, left posterior ventricular branch, circumflex branch, diagonal branch, and anterior interventricular branch). The great cardiac vein (GCV) ran beneath the anterior interventricular branch in 56 specimens out of 103, beneath the diagonal branch in 75 specimens out of 103, and beneath the circumflex branch in 36 specimens out of 103, while the other CV mostly ran over CA. The present observations suggest that the CV on the right side may be formed prior to CA, while the CV on the left side may be formed simultaneously with CA.

Time‐saving and fail‐safe dissection method for vestibulocochlear organs in gross anatomy classes

Because the vestibulocochlear organs are tiny and complex, and are covered by the petrous part of the temporal bone, they are very difficult for medical students to dissect and visualize during gross anatomy classes. Here, we report a time‐saving and fail‐safe procedure we have devised, using a hand‐held hobby router. Nine en bloc temporal bone samples from donated human cadavers were used as trial materials for devising an appropriate procedure for dissecting the vestibulocochlear organs. A hand‐held hobby router was used to cut through the temporal bone. After trials, the most time‐saving and fail‐safe method was selected. The performance of the selected method was assessed by a survey of 242 sides of 121 cadavers during gross anatomy classes for vestibulocochlear dissection. The assessment was based on the observation ratio. The best procedure appeared to be removal of the external acoustic meatus roof and tympanic cavity roof together with removal of the internal acoustic meatus roof. The whole procedure was completed within two dissection classes, each lasting 4.5 hr. The ratio of surveillance for the chorda tympani and three semicircular canals by students was significantly improved during 2013 through 2016. In our dissection class, “removal of the external acoustic meatus roof and tympanic cavity roof together with removal of the internal acoustic meatus roof” was the best procedure for students in the limited time available. Clin. Anat. 30:703–710, 2017.

A study of fundamental courses in the great cardiac vein

We studied an extremely rare great cardiac vein anomaly in a 65-year-old woman during dissection practice at the Akita University School of Medicine (2013). The great cardiac vein has two main roots, one accompanied by a left marginal vein that pours into the coronary sinus, and the other ascending along the anterior interventricular sulcus from the apex, and running over the circumflex branch of the left coronary artery. It then runs along the atrial side of the transverse sinus of the pericardium, and drains directly into the superior vena cava. No anastomosis between these veins was evident. The great cardiac vein might originate from two venous systems, one in the posterior wall of the left ventricle, and the other running along the anterior interventricular sulcus. These venous systems flow in the venous network of the left edge of the coronary sulcus. The former venous system always selected the course, which went to the coronary sinus in the venous network. The latter system may drain into one of the following four courses: the first one contacts the former course; the second passes to the transverse sinus of the pericardium and flows to the (right) superior vena cava; the third passes between a pulmonary trunk and ascending aorta from the dorsum of the pulmonary trunk, turns around in a ventral aspect, and then flows into the left superior vena cava; and the fourth flows to the anterior cardiac vein. The first of these belongs to the normal great cardiac vein, but the others are anomalous.

Anomalous head of the brachial muscle penetrates the deltoid muscle

We report here, for the first time a specimen in which the insertion of the deltoid muscle is divided into two parts, composing a canal. The brachial muscle was composed of medial, lateral, and anomalous heads. The anomalous head arose as a thin tendon from the surgical neck of humerus, passed through the canal, and then became confluent with the lateral head. The musculocutaneous nerve innervated the brachial muscle. The lateral head, but not the anomalous head, received a thin branch from the radial nerve.

The Embryonic Ascent of the Kidney Revisited: Embryonic kidney ascent

Although the embryonic kidneys ascent is well established, the intermediate morphological changes that occur during the process are unclear. To evaluate the morphological events that accompany the kidneys ascent, we examined serial sagittal sections from 24 embryos at 5–7 weeks gestation. Six specimens had bilaterally ascending kidneys that were between the levels of the second to fifth lumbar vertebrae, and each kidney had a primitive renal cortex surrounding clusters of ampullae, which branched from the pelvis, and a dense tissue band that connected the renal cortex with the embryonic adrenal cortex or celiac ganglia, and there was no adipose capsule or renal artery. The tissue band contained abundant nerve twigs from the major splanchnic nerve; thus, it was conceivable that it was sufficiently rigid to support the length of the retroperitoneal tissue mass that included the embryonic adrenal cortex, celiac ganglia, and kidney. The lumbar vertebral bodys height was much shorter than that of the ascending kidney. However, the lower vertebral columns curvature was often maintained, even when the kidneys had ascended. Therefore, vertebral column straightening was not the only factor required to drive the ascent. Together with the growth of the thorax and liver, the adrenal cortex, ganglia, and kidney appeared to change simultaneously at a position relative to the vertebrae. The renal artery established a connection to the renal cortex after the ascent. Evaluations of frontal sections from five additional specimens suggested that from its initial position, the kidney extended upwards between bilateral umbilical arteries. Anat Rec, 302:278–287, 2019.

Simple ways to dissect ciliary ganglion for orbital anatomical education

In the case of anatomical dissection as part of medical education, it is difficult for medical students to find the ciliary ganglion (CG) since it is small and located deeply in the orbit between the optic nerve and the lateral rectus muscle and embedded in the orbital fat. Here, we would like to introduce simple ways to find the CG by 1): tracing the sensory and parasympathetic roots to find the CG from the superior direction above the orbit, 2): transecting and retracting the lateral rectus muscle to visualize the CG from the lateral direction of the orbit, and 3): taking out whole orbital structures first and dissecting to observe the CG. The advantages and disadvantages of these methods are discussed from the standpoint of decreased laboratory time and students as beginners at orbital anatomy.

Abnormal veins around the heart with the closure of the coronary sinus ostium

In a cadaveric dissection course at Akita University Graduate School of Medicine in 2014, we observed abnormal veins in a 72-year-old male who died of prostate cancer. The abnormality consisted of the following: closure of the opening of the coronary sinus (closure of the coronary sinus ostium), a persistent left superior vena cava (Lsvc), and a postaortic left brachiocephalic vein (Palbv). The shunt between the coronary sinus and left atrium was not observed. The blood of the coronary sinus flowed into an oblique vein of the left atrium, which was wide and reverse-funnel shaped, penetrated the pericardial sac then continued to the Lsvc. The anastomotic veins between the Lsvc and the (right) superior vena cava were seen to consist of two veins as follows: one was a left brachiocephalic vein, the other a dorsal postaortic left brachiocephalic vein (dorsal Palbv). The dorsal Palbv passed dorsally on the ligamentum arteriosum, and then passed between the ascending aorta and the trachea. The dorsal Palbv was thicker than the left brachiocephalic vein. We discuss the process of formation of these variations.