No abstract

Rather than the usual mammalian scheme in which tendon and sheath surfaces provide as little friction as possible, the tendons and sheaths of many bats have a locking segment on the manual and pedal flexor tendon complex. This tendon locking mechanism (TLM) exists opposite the proximal phalanges of each toe and pollex of many bats. Its structure, similar to a ratchet mechanism, assists bats in hanging with little muscular effort. The third digit of the pelvic limb and the pollex of species representing 15 chiropteran families were studied to determine the presence or absence, morphology, and function of the TLM. Most of the species studied have a TLM consisting of a patch of tubercles on the ventral surface of the flexor tendon associated with the proximal phalanx of each pollex or toe. The sheath adjacent to this portion of the flexor tendon has a series of transverse folds or ridges, which, when engaged with the tubercles on the tendon, lock the tendon in place. The TLM is similar in megachiropterans and microchiropterans possessing it. The TLM is absent, however, in some of the microchiropterans studied, most notably in the phyllostomids. Since many birds have a TLM similar to that of bats, it is an excellent example of the convergent evolution of a feature brought about by similar functional pressures on birds and bats.

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 and Kerivoula 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.

Although there is a great amount in the literature to describe the anatomy of the parotid gland as a whole, little attention is given to the parotid duct. The purpose of this study is to examine the surgical anatomy of the parotid duct with special emphasis placed on the major tributaries forming the parotid duct and the relationship of the facial nerve to the duct. Twenty-nine fresh cadaver halves were dissected and the branching pattern of the ducts, position within the parotid, and their relationship to the facial nerve were studied. Of the complete heads studied, the parotid duct had the same pattern in 78.6% on the right and left sides. The parotid ducts in 31.0% of the half heads presented as a single discernible duct from parotid papilla to within the gland. In 62.1% of the half heads, the ducts were formed by a branching pattern within the gland. In the ducts with a branching pattern, 48.3% displayed a bifurcated pattern, 6.9% were trifurcated, and 6.9% had multiple branches. In 6.9% of the half heads studied, the parotid ducts bifurcated distal to the parotid gland. In all cases, the deep lobe of the parotid enveloped the parotid duct; only small ductules connected the superficial lobe with the duct. The facial nerve and its branches were always observed lateral to the parotid duct. Because one dissects lateral to the facial nerve during a superficial parotidectomy, generally the parotid duct remains intact and potential complications such as facial paralysis, sialoceles, and fistulizations are thereby minimized.

Since the introduction of the term "fascia transversalis" by Sir Ashley Cooper in 1840, this thin layer of tissue has been discovered, denied, and redefined. The transversalis fascia was originally described as a bilaminar membrane. Although most subsequent descriptions do not reflect this analysis, some authors, especially in the surgical literature, believe that a posterior lamina of the transversalis fascia exists. Others believe that the posterior lamina of the transversalis fascia is, in fact, part of the preperitoneal fascia. The usefulness of the transversalis fascia and its derivatives or analogues; e.g., the crura of the deep inguinal ring, have also been extensively discussed. The aim of this paper is to provide a brief survey of the historical literature concerning the transversalis fascia and a discussion of some of the contemporary views on its morphology and significance in current laparoscopic hernia repair.