DISSECTION OF THE DOG 97 



A. poplitea. — The popliteal artery continues the femoral between the 

 two heads of the gastrocnemius muscle, and insinuates itself between the 

 popliteal muscle and the joint-capsule of the articulation between the femur 

 and tibia. In order to follow the artery to its termination it is necessary to 

 reflect the popliteal and long flexor muscles. This having been done, 

 it will be found that the popliteal ends by dividing into the anterior 

 and posterior tibial arteries. The latter is so small that, to all intents 

 and purposes, the anterior tibial is the direct continuation of the parent 

 vessel. 



A. tibialis anterior. — The anterior tibial artery soon pierces the liga- 

 mentous membrane between the tibia and fibula and thus gains the anterior 

 tibial region, where its further course has been previously noted. 



The sole of the pes. — Before any dissection is performed, five areas of 

 modified skin should be noted. These are in the form of distinct, callous, 

 hairless projections ; one of them, the largest, lies in the hollow of the digits. 

 Its form is that of a heart with the apex distal. The four smaller callosities 

 lie over the joints between the second and third phalanges of the second, third, 

 fourth, and fifth digits. 



The skin over the sole should now be removed and the structure and con- 

 nections of the callosities determined. Each callosity consists of a fibro-fatty 

 basis with which thick, horny, papillated skin is intimately connected. The 

 callosities are joined to the sheaths of the flexor tendons by strong ligamentous 

 bands. This is more particularly noticeable in connection with the large 

 callosity, which also receives a bifurcating band from the tendon of the deep 

 flexor muscle. 



Muscles and tendons of the sole. — The muscles and tendons of this 

 part of the pes are arranged in the following layers : 



1st Layer. — M. flexor digitorum brevis, m. abductor digiti quinti. 



2nd Layer. — Tendon of the m. flexor digitorum profundus, mm. lumbricales, 

 m. quadratus plantss. 



3rd Layer. — M. adductor digiti quinti, m. adductor digiti secundi, mm. 

 interossei. 



4th Layer. — Tendon of m. peronssus longus. 



In the dissection of the most superficial layer an examination must be made 

 of the sheaths of the flexor tendons. The sheaths assist the bones of the 

 digits in the formation of osseo-membranous tubes in which the flexor tendons 

 are contained. The dorsal wall of the tube is formed by the metatarsal sesa- 

 moids and the phalanges ; while the plantar portion of the tube is formed by 

 the flexor sheaths which are attached to the margins of the above bones. The 

 sheaths are not of uniform strength throughout. On a level with the sesamoid 

 bones, and opposite the distal end of the first phalanx, a considerable accession 



