Thomas H. Quinn

The digital tendon locking mechanism of the avian foot (Aves)

SummaryRepresentatives of all avian orders were studied in order to establish that the tendon-locking mechanism (TLM), consisting of local specialization of the flexor tendons and the adjacent portion of the flexor tendon sheath, is by no means rare, but rather, constitutes the prevalent condition in a large majority of the avian species sampled. The areas of tubercles on the tendons and the adjacent sheath plications intermesh with one another thereby forming a true tendon-locking mechanism that maintains the distal and other interphalangeal joints of the digits in the flexed position. The TLM seems to function not only in perching, but in a wide variety of other activities of the avian foot including swimming, wading, prey-grasping, clinging, hanging, and tree climbing. The basic structural components of the mechanism are remarkably similar in the divergent avian groups adapted for these activities. Ultrastructural detail of the TLM was studied by means of scanning and transmission electron microscopy. Interdigital variation in distribution of the TLM in all of the digits of individuals were made as were comparisons of the interspecific distribution of the TLM. An analysis of the biomechanics involved in engaging the elements of the TLM and how they produce locking of the flexed joints of the digits includes a consideration of the roles of the podothecal pads, ungual flexor processes, and the elastic flexor and extensor ligaments of the toes. The components of the TLM are differentiated in early fetal development establishing that the TLM components are not acquired adventitiously in response to such factors as posthatching mechanical stresses.

Evolution of the digital tendon locking mechanism in bats and dermopterans: A phylogenetic perspective

A tendon locking mechanism (TLM) in the digits of the feet has been described previously only in bats and birds. In bats, this mechanism typically consists of a patch of tuberculated fibrocartilage cells on the plantar surface of the proximal flexor tendons, and a corresponding plicated portion of the adjacent flexor tendon sheath. The two components mesh together like parts of a ratchet, locking the digit in a flexed position until the mechanism is disengaged. This system apparently allows bats to hang for long periods of time with reduced muscular activity. In this study, we document for the first time the presence of a similar tendon lock in dermopterans, an occurrence that provides additional support for the hypothesis that dermopterans and bats are sister taxa. The present work also includes observations on the morphology of the digital tendon system in chiropteran species not previously examined, including members of the Craseonycteridae, Mystacinidae and Kerivoulinae. Unlike other bats that have a TLM,Craseonycteris andKerivoula have a plicated proximal tendon sheath but lack distinct tubercles on the flexor tendon. This condition may be related to small body size or may represent an evolutionary intermediate between the presence of a well-developed TLM and the complete absence of this structure. Phyllostomids apparently lack the ratchet-like TLM typical of other bats, instead exhibiting modifications of the tendon sheath that may contribute to its function as a friction lock. Consideration of the distribution of TLM structures in the context of previous phylogenetic hypotheses suggests that a ratchet-type tendon lock was lost and reexpressed at least once and perhaps several times within Microchiroptera. The friction lock is an autapomorphy of Phyllostomidae.

The collar plexus of subcutaneous thermoregulatory veins in the pigeon, Columba livia; its association with esophageal pulsation and gular flutter

SummaryHeat stressed pigeons dissipate heat by panting and gular flutter which is associated with upper esophageal pulsation; these activities depend on evaporative cooling and convection from mucosal surfaces. The collar plexus, an unusual subcutaneous system of erectile veins, is the specialized vascular apparatus that seems to serve as the heat exchanger for gular flutter and upper esophageal pulsation. The collar plexus lies between the dermis and a deeper muscle sheet, extending from the head to the thoracic inlet in mature pigeons. The slightly filled plexus is inconspicuous, resembling an ordinary venous bed, and consists of thick-walled veins having small lumina, similar to arteries. When moderately-filled, the veins of the plexus distend and abruptly transform into “beaded” veins with contorted, sacculated expansions separated by constricted segments.During heat stress, engorgement of the plexus occurs rapidly by continual flow over arteriovenous anastomoses that empty arterial blood directly into the beaded veins. Constriction of veins draining the plexus impedes venous return to the jugular veins, thereby maintaining tumescence of the plexus. Disgorgement of the plexus also occurs abruptly. Intimate contact between the deep aspect of the engorged plexus and the trachea and upper esophagus provides for heat transfer from the plexus to the mucosal surfaces of these structures where evaporative cooling takes place. During esophageal pulsation the esophageal surface extends and augments the respiratory dead-space area used for evaporative cooling. Thus a possible advantage of cooling by upper esophageal pulsation is that, like gular flutter of the oropharynx, it may minimize the amount of air that must pass over gas exchange surfaces, thereby limiting the washout of CO2 and consequent acid-base disturbances that occur during panting in extreme heat stress.Ability to inflate the esophagus is of general occurrence among the pigeons and doves (Family Columbidae). The collar plexus is also widespread, having been found in representatives of five of the examined six main subdivisions of the Columbidae.

Intracranial distribution of the sympathetic system in mice: DiI tracing and immunocytochemical labeling

The intracranial distribution of the cephalic branches of the superior cervical ganglion (scg) was studied in mice using indocarbocyanine dye (DiI) anterograde tracing. Two main branches were traced from the scg. The first branch joined the nerve of the pterygoid canal (the vidian nerve), npc, from which several intracranial sympathetic branches passed to the branches of the trigeminal nerve (tgn), abducent nerve (abn), trochlear nerve (trn), and oculomotor nerve (ocn). Most of the second branch joined the abn, from which sympathetic fibers dispersed in the distal region of the trigeminal ganglion (tgg) to form a plexus close to the ganglions branches. Branches from this plexus joined the branches of the tgn, trn, and ocn. Several minor branches arising from the second branch of the scg were also observed. One formed a sympathetic plexus around the internal carotid artery (ica); a second formed a sympathetic plexus in the proximal region of tgg, close to its root; and a third branch coursed laterally to reach the ear by passing along the greater petrosal nerve (gpn). All of the intracranial trajectories traced from scg were found to be catecholaminergic, and likely sympathetic, using tyrosine hydroxylase (TH) immunocytochemistry. Anat Rec 263:99–111, 2001.

Additional mechanisms of hiatal hernia recurrence and its prevention

SummaryThe conventional hiatal hernia repair is a tension repair. Large defects such as those associated with an intrathoracic stomach can have a high rate of recurrence resulting in esophageal symptoms and in some instances gastric strangulation. Numerous additive procedures are used to secure the stomach in the abdominal cavity including mesh buttressing, fundoplication, anterior abdominal wall gastropexy and fundus diaphragmatic suture fixation. The optimal repair is unknown primarily because crura closure failure is poorly understood. A literature review was used to determine the proven causes of hiatal hernia recurrence. Early postoperative vomiting, surgeon inexperience, short esophagus and no crus closure are documented causes. In a series of 19 hiatal hernia recurrence repairs from our institution, additional causes such as suture pull-out and trauma have been established as additional mechanisms of recurrence. Increased intra-abdominal pressure associated with motor vehicle accidents was the precipitating factor in 2/19 patients. Suggested methods for prevention of hiatal disruption and resultant hernia are proposed which include: a postoperative antiemetic regimen, restricted activity in the early postoperative period, an assessment technique for the short esophagus when utilizing a laparoscopic approach, crus closure calibration and inclusion of the diaphragmatic fascia when performing hiatal closure for large paraesophageal hernias and the short esophagus.

Diethylstilbestrol, teratogenesis, and carcinogenesis: Medical/legal implications of its long-term sequelae, including third generation effects

The spectrum of teratogenic and carcinogenic effects which can be exerted when the unborn child is exposed to diethylstilbestrol (DES) has been shown to be broad. Animal work indicates the need for vigilance as regards genetic susceptibility to DES sequelae. The emergence of third generation sequelae has been demonstrated in mice, and has been postulated to occur in humans. Given the emergent data establishing problems of infertility in men and women and of relatively late onset cancer, and the possibility that in utero exposure to DES may prime a variety of tissues to noxious environmental influences there is an urgent need for measures to provide just coverage for those harmed by the drug. The DES disaster also raises important ethical and reserch questions which demand attention.

The maxillary artery as a recipient vessel option for complex midface and anterior skull base microsurgical repair: A cadaveric study

Variations in the operative situation for complex head and neck defect reconstructions resulting from mechanisms such as trauma, oncologic resection, and prior radiation exposure can result in situations of a vessel‐depleted neck. This requires an awareness of alternate, innovative options for use in reconstructive repairs. The purpose of this study was to provide characterization of the third segment of the maxillary artery necessary to consider its use as a recipient vessel in free flap repair of complex midface defects.

Surgical Anatomy of the Inguinal Region from a Laparoscopic Perspective

In 1969, Ravitch stated that the “operations for the cure of hernia would seem to be established and well known beyond the possible need for further discussion and demonstration.”2 Actually, before the introduction of laparoscopic surgery, the “problem hernia” seemed to be well defined. The term indicated “the protrusion of a loop or knuckle of an organ or tissue through an abnormal opening,”3 that needed to be repositioned and kept in place with some type of repair. The only variable factor was the choice of herniorrhaphy. Today, laparoscopic hernia repair challenges the surgeon with a new perspective of hernia.