MUSCULAR SYSTEM 99 



the tail in the lower Mammals, and is therefore termed in them 

 the abductor caudalis. 



The curvator coccygis, which is met with on the anterior 

 surface of the lower sacral and sometimes of the upper caudal 

 vertebrae, belongs to this same category. It corresponds with 

 the depressor caudae of the lower Mammals. 



The vestigial character of all these muscles is in several ways 

 evident. They vary in form and size, and may be partly or 

 wholly replaced by fibrous tissue, or, finally, one or other of 

 them may be altogether wanting. This is also the case in the 

 Anthropoids, where (e.g. in the Orang) their vestigial character is 

 in some ways more pronounced than in Man. 



Another caudal muscle may here be referred to, although 

 morphologically it does not belong to the above-mentioned series. 

 This is the caudo-femoralis (agitator caudae) which, in a large 

 number of Mammals (Monotremata, Marsupialia, most Carnivora, 

 Lemuroidea, and tailed Monkeys) plays a great part, as flexor 

 and abductor of the tail when the thigh is fixed, and which, in 

 exceptional cases, appears in Man also. It lies at the lower edge 

 of the gluteus maximus, being separated from it by only a small 

 space. It arises from the lateral edge of the coccyx or of the last 

 sacral vertebra, and is inserted into the femur below the point of 

 attachment of the lowest bundle of the gluteus. 



Normally, this muscle is wanting in Anthropoids, but it is 

 not improbable that it may occasionally reappear in them as in 

 Man. 



In both the dorsal and ventral trunk muscles we find indica- 

 tions of original segmentation. In the intercostal muscles the 

 segmentation is completely retained, and not infrequently tendons 

 pass from the ends of the lower ribs into the broad abdominal 

 muscles. Cartilaginous tracts are sometimes found persisting in 

 a line with these tendons, but nearer the median plane, and 

 they may be either free or connected with the tendons. Even 

 in cases where all such indications are wanting, the innervation 

 of these muscles points to a primitive metamerism. 



In the same way, the rectus abdominis, by its " inscrip- 

 tiones tendineae," shows a more or less distinct segmentation. 



This muscle in the lower Vertebrates (e.g. tailed Amphibians) 

 extends from the pelvis to the head region ; but in the higher 

 Vertebrates, and particularly in Mammals, in accordance with 

 advancing modification, and especially with the intervention of 

 the sternal apparatus, it has become divided into a posterior and 



