212 HISTORY OF THE HUMAN BODY 



tions from the intervertebral system. The rectus capitis 

 posterior minor, in the form of a pair of small slips, extends 

 between the rudimentary spine of the atlas and the occipital 

 bone, and a similar but somewhat larger pair, rectus capitis 

 posterior major, extends from the spine of the axis to the 

 occipital bone, embracing the other pair. An obliquus capitis 

 inferior extends from the spine of the axis to the transverse 

 process of the atlas, and an obliquus capitis superior continues 

 from this point to the occipital bone. 



This entire group develops from what appears in reptiles as 

 a single mass. The dorsal branch of the second cervical nerve 

 runs through this mass and divides it into medial and lateral 

 portions. From the former both recti (major and minor) 

 develop, through a longitudinal separation of their fibers, and 

 from the latter arise both obliqui, which become separated from 

 one another through the outward growth of the transverse 

 process of the atlas, which has divided the muscle across its 

 fibers, a perfect example of the principle designated above as 



i (&)., p. i 9 8. 



Posterior to the pubo-ischiadic symphysis and the cloacal 

 orifice, structures which make an hiatus in the ventral series 

 of axial muscles, both dorsal and ventral masses become re- 

 duced in size and taper down to form the musculature of the 

 tail. But little morphological research has been devoted to 

 this region, and even in mammals, where the conditions seem 

 the best known, there is much to be done to complete the sub- 

 ject. In long-tailed mammals there are typically two ext en- 

 sores caudce upon each side of the mid-dorsal line ; an extensor 

 caudce medlalis, which is a direct continuation of the multifidus 

 and an extensor caudce later alis, which appears between multi- 

 Hdus and longissimus, but does not seem to be a continuation of 

 either. Upon the sides are two abductores caudce, dorsalis 

 and ventralis, the former being short and of lesser functional 

 importance, the latter assuming the function of the principal 

 abductor. Ventrally there is a single pair of ftexorcs (de- 

 pressores) caudce. Of the above, as shown by the innerva- 

 tion, the extensors and dorsal abductors belong to the dorsal 



