RUDIMENTARY ORGANS OF ANIMALS 119 



3. The Muscular System. The cutaneous muscles, 

 those of the shell of the ear, and those that move 

 the tail, which in most mammals are well developed, 

 are still present in man, but have degenerated. 



Further, there is to be found in man the 

 intra-acetabular part (the round ligament) of the 

 deep flexor muscle of the toes which is functional 

 in some animals in young ostriches, for instance. 

 In the adult ostrich the intra-acetabular part is 

 separated from the rest of the muscle, which is 

 attached to the pelvis. Traces remain in the 

 horse of a connection between the intra- and the 

 extra-acetabular parts ; the muscle itself is divided 

 into two parts, the pectineal muscle in the thigh, 

 and the deep flexor muscle of the toe situated in 

 the leg. In the orang-outang, this degeneration 

 has made further advances than in man, the intra- 

 acetabular part of the muscle having entirely 

 disappeared. 1 



4. The Nervous System. Here we find numerous 

 signs of degeneration, of which the following are 

 a few examples : 



In the brain the pineal gland, the last remaining 

 vestige of what was formerly a functional eye, is 

 present. 



In the spinal cord the filum terminate still 

 exists. We know that the spinal cord in man does 

 not retain its normal thickness to the extremity of 



1 See Sutton, Ligaments, their nature and morphology. London, 



1887, 



