254 ZOOTOMY. 



333. In the second digit the arrangement is similar, except that the 

 first or superficial perforated tendon, instead of forking, forms a 

 sheath for the other two tendons at the proximal end of the first phalanx. 



334. In the first digit or hallux, there are only two flexor tendons ; 

 of these the perforating tendon is superficial, and the perforated forms a 

 sheath for it at the proximal end of the first phalanx. 



335. The perforating tendons of the second, third, and fourth digits 

 are all formed by the trifurcations of a single tendon, lying deeper 

 than the perforated tendons, and belonging to a large muscle, the 

 peroneus medius : this tendon is joined by a slip from that of 

 the flexor perforans, which is continued to form the perforating 

 tendon of the hallux. 



336. The ambiens, a small, slender muscle, lying superficially on 

 the inner surface of the thigh, just over and parallel to the femur : it 

 arises from the pubis immediately ventral to the acetabulum : distally it 

 passes into a long, slender tendon, which, on reaching the knee, pene- 

 trates the fibrous capsule of the joint, curves round to the outer side, 

 passing at the same time distalwards, and finally joins the flexor 

 perforatus of the second and third digits. 



337. If, on the undissected side, where the tendons are 

 not displaced, the shank is flexed on the thigh and the 

 tarso-metatarsus on the shank, as in perching, the toes will 

 undergo complete flexion : this is chiefly due to the fact that 

 in the flexion of the tarso-metatarsus on the shank the flexor 

 tendons of the toes are put upon the stretch as they pass 

 the mesotarsal articulation (§ 117): it is also aided by 

 the flexion of the shank upon the thigh producing tension 

 of the ambiens tendon, which, in its turn, acts upon the 

 flexors of the digits. 



LV. In the hardened brain notice the following external 

 characters : 



338. The medulla oblongata (Fig. 58, m.o), con- 

 tinuous behind with the spinal cord, and like it composed 

 externally of white matter : ^ it greatly exceeds the cord in 



^ The distinction between white and grey matter is not obvious in the , 

 hardened brain ; it is therefore convenient to have a freshly removed 

 brain for comparison. 



