Herbert H. Srebnik

Introduction to the Lymphatic System

The lymphatic system is a collection of vessels, nodes, and organs including the pharyngeal lymphoid ring. Lymph, the fluid flowing through the system, is colorless (L., lympha = clear water) and the vessels normally containing it are usually collapsed and difficult to isolate. Hence, the lymphatic system is frequently perceived as being less important than other systems of the body and, in general, given short shrift in textbooks of topographic anatomy. Actually, of course, the lymphatic system is a vital cog in the homeostatic machinery of the body. One of its functions is to return to the blood vascular system fluids and plasma proteins that were filtered or forced out at the arterial end of capillaries and lost to tissue spaces. By returning extravasated plasma proteins, especially albumins, to the blood stream, the lymphatic system helps maintain plasma osmotic pressure and, thus, the fluid balance between blood and the interstitial spaces.

The Thoracic Cage

The thoracic cage is the protective armor that shields the heart, lungs, and great vessels as well as many abdominal organs. The liver, gall bladder, and spleen, to name just a few, lie under the cover of ribs, because the concavity of the dome-shaped diaphragm is part of the abdominal cavity.

The Anterior Abdominal Wall

The subcostal body wall is largely muscular in its overall construction. The muscles not only function in their usual capacity as movers of the skeleton, e.g., they flex and rotate the trunk, but also provide support and protection for abdominal contents. In addition, a muscular body wall is able to accomodate to variations in intra-abdominal pressure and to comply with changes in size, shape, or position of internal organs, e.g., an enlarging uterus of pregnancy.

On Form and Function

A great deal has been written on this subject, and you are probably familiar with the expression “Form follows Function”—meaning, structure is designed for the use to which it is put. Leonardo da Vinci (1452–1519), quite possibly the most creative genius of his day, referring to the relationship between muscle size and function, concluded: “In all the parts where man has to work with greater effort nature has made the muscles and tendons of greater thickness and breadth” (Dell’ Anatomica Fogli A, Royal Library, Windsor). The musculoskeletal anatomy of the limbs is particularly well suited to illustrate and illuminate the anatomical basis of function, for both upper and lower extremities are structurally adapted for maximal effectiveness: the former to be used as a prehensile organ, and the latter to provide the means of support for upright posture and locomotion. Crucial to an understanding of their functional capacities is a knowledge of their bony infrastructure.

Fields of Lymphatic Drainage

This section is an extension of chapter 17, which introduced you to the descriptive, functional, and clinical anatomy of the lymphatic system. We now continue that discussion by examining vessels and nodes engaged in the lymphatic drainage of the thorax, abdomen, and pelvis, and conclude with the general plan of lymphatics draining upper and lower limbs.

Innervation of Upper Limbs

This chapter begins with a short review of human limb development, and of the evolutionary process that causes flexor and extensor surfaces of upper and lower limbs to become transposed—thus, to face in opposite directions. It then discusses the composition and functional organization of the brachial plexus, refers to brachial plexus injuries, and comments on the cutaneous innervation of the upper extremities. A thorough description of the lumbosacral plexus and its branches appears in chapter 32, “Innervation of Lower Limbs.”

The Urogenital Triangle

The urogenital triangle is another complicated and relatively inaccessible region of the human body; it is difficult to dissect and perhaps even more difficult to explain (now more so than ever, for the 1998 revision of the Nomina Anatomica has abandoned the term urogenital diaphragm to describe a key structure in the urogenital triangle). We’ll start by taking a close look at the myofascial anatomy of the urogenital triangle, then review and amplify the developmental history of the urogenital sinus to explain sex differences in the region. The rest of the chapter will be devoted to a discussion of perineal spaces and fasciae relevant to clinical anatomy.

Functional Anatomy of the Shoulder Joint

The shoulder joint is designed to provide maximum mobility to the upper limb. Its range of motion is approximately 180° in the frontal plane—i.e., the fully adducted limb can be raised high above the head. Perhaps even more impressive is the joint’s capacity for circumduction during which the arm traces in circular motion the outline of a cone whose apex is the shoulder (see Fig. 1.4, p. 7).

Formation of Urogenital System

The primary source of the urogenital system is intermediate mesoderm. It first appears, you will recall, in the presomite embryo, during the third week of human development (Fig. 4.2, p. 25). Embryonic mesoderm simultaneously gives rise also to paraxial and lateral plate mesoderm. In the early embryo, intermediate mesoderm is located, bilaterally, between the other two forms of embryonic mesoderm; and, like paraxial mesoderm, it becomes transversely segmented without, however, differentiating into somite-like blocks of tissue.

Myofascial Anatomy of the Perineum

The perineum is the subpelvic region, thus the “bottom” of the trunk. Its boundaries are: the pubic symphysis in front and the coccyx behind; the ischiopubic rami anterolaterally; and the paired sacrotuberous ligaments (between sacrum and ischial tuberosities) posterolaterally (Fig. 27.1).