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 
vertebre, belongs to this same category. It corresponds with 
the depressor caudee 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 caude) 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 tendinez,” shows a more or less distinct segmentation. 
This muscle in the lower Vertebrates (¢.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 
