J. Playfair McMurrich 47 



Before passing to a consideration of the nerve-supply of tliese muscles 

 a few remarks may be made in the way of a comparison of the plantar 

 nponciirosis of the lacertilia with that of the amphibia. In the latter, 

 just as was the case with the palmar aponeurosis, it forms a continuous 

 sheet which receives the insertion of the crural flexors and gives origin 

 to the plantar muscles of the pes, the only indications of a layered con- 

 dition to be seen in it being at its upper and lower borders, where it 

 becomes partly divided into subjacent layers corresponding to the layers 

 of muscles inserting into or arising from it. In the lacertilia the con- 

 ditions are slightly different. Covering the posterior surfaces of the 

 plantaris superficialis lateralis there occurs a distinct aponeurotic layer 

 (Figs. 4 and 5, a) which receives the insertion of the fibers of that 

 miiscle and is also joined by the tendon of the plantaris superficialis 

 medialis. As it is traced downwards this aponeurosis separates in the 

 neighborhood of the ankle joint into a thinner and narrower superficial 

 layer and a thicker and deeper layer. The former gradually verges 

 towards the fibular side as it passes into the foot and is. finally lost over 

 the outer side of the fifth metatarsal bone. The deeper layer gives rise 

 from the deep surface of its medial half to the superficial layer of the 

 plantar muscles, while its lateral portion, developing a sesamoid cartilage 

 which receives the insertion of the fibers of the plantaris superficialis 

 lateralis, inserts into the fifth metatarsal. 



In addition to this superficial layer a deeper layer of the aponeurosis 

 also occurs (Figs. 4 and 5, a'), this being the aponeurosis with which the 

 plantaris profundus III-II becomes connected and which is continued 

 onward as the tendons of that muscle to be inserted into the terminal 

 phalanges of the digits. 



There are then in the lacertilia two principal portions of the plantar 

 aponeurosis as compared with the continuous aponeurosis of the amphi- 

 bia. A deeper portion has separated from a more superficial one to 

 form the tendons of the plantaris III-II and having also inserted into 

 it portions of the plantaris superficialis. Probably too the tendon of 

 insertion of the plantaris profundus I, on account of its attachment to 

 the sesamoid bone developed in the tendon of the plantaris profundus 

 III-II, is to be regarded as a separated portion of the original aponeu- 

 rosis and, if this be the case, all the crural flexors primarily insert into 

 the plantar aponeurosis as in the amphibia. 



Turning now to the nerves of the crus. In sections just above the 

 knee the sciatic nerve is represented by three trunks. One of these 

 (Fig. 6, A), when traced onwards, curves around the outer border of 

 the fibula to the dorsal surface of the crus and need not concern us 

 further. The other two are supplied to the flexor surface. 



