68 Proceedings of the Royal Irish Academy. 



from the three upper dorsals and four lower cerTicals, and being in- 

 serted into the basiocc-ipital.'^'' 



Rectus capitis anticus minor extended from the transverse process 

 of the atlas to the lateral ridges of the same bone, close beside the in- 

 sertion of major. 



Rectus capitis posticus major and minor were both normal in their 

 attachments, but feebly developed, the latter being the stronger of the 

 two. 



Eectus capitis lateralis was moderately strong. 



Obliquus capitis inferior was enormous, a condition, probably, to 

 be correlated with the necessity for combined lateral and downward 

 motion of the head.f 



Scalenus medius, with scalenus posticus inseparable from it, arises 

 from the transverse processes of all the cervical vertebrae except the 

 atlas, and is inserted into the first and second ribs, some of the fibres 

 belonging to the former being continuous with the fibres of origin of 

 rectus thoracicus lateralis, which from this origin passes down to be 

 inserted into the eighth and ninth ribs ; it is placed anteriorly to ser- 

 ratus magnus and externally to rectus abdominis, which is inserted 

 into the fifth, sixth, seventh, and eighth sternal ribs, and has its fibres 

 directed upwards and slightly outwards, overlapping the normal inter- 

 nal intercostals. 



Sternocostalis arises from the presternum and four upper mesosternal 

 stern ebrse, and is inserted into the second, third, fourth, fifth, and 

 sixth ribs. 



Iliocostalis sends a tendon to every rib, and has a cervical prolonga- 

 tion, as has longissimus dorsi, which is very large. 



Serratus posticus inferior arises from the lumbar fascia, and is in- 

 serted into the ribs, from the thirteenth to the twenty-third inclusive. 



Sternomastoideus and cleidomastoideus are curiously related to one 

 another ; they are both inserted into the partimastoid process, separated 

 only by the spinal accessory nerve ; the former arises from the an- 

 terior surface of the sternum, and from the mesoseapular segment 

 between the clavicle and the sternum. On its way upward it detaches 

 a slip from its hinder border, which runs into the cleiodomastoid 

 (origin middle of clavicle), which in turn gives off a slip to the superior 

 trapezius. 



Thus it will be seen that both muscles are distinctly represented 

 here, the only trace of union being the transverse band. In Arctopi- 

 thecus a single muscle exists arising from the sternum, but betraying its 

 compound nature by its two slij)s of insertion into the paramastoid; in 

 Bradypus there is manifestly a sternocleidomastoid, for here the oiigin 



* A some-what similar, but more restricted origin (sixth, seventh, and eighth 

 cervicals) exists in Arctopithecus BlainvUlei. Vide Proceedings Royal Irish Aca- 

 demy, A^ol. I., Series II. (Science), page 619. 



t This muscle was also well developed in Arctopithecus {loc. cit.). 



