OCR Text |
Show 1896.] MYOLOGY OF RODENTS. 189 11. The gracilis is usually double in the Myomorpha, single in the Sciuromorpha. 12. The accessorius is usually absent in the Myomorpha, always present in the Sciuromorpha. With a view to comparing the myology of the Lagomorpha with the other suborders, I dissected the muscles of a Hare and a Rabbit, but have refrained from enlarging this paper with a detailed description of these muscles because they have already been described by other authors. Differences between the Myomorpha and the Lagomorpha. 1. In the Myomorpha the different parts of the temporal are closely connected. In the Lagomorpha the orbital part is large and much separated from the rest. 2. In the Myomorpha the anterior deep part of the masseter passes through the infraorbital foramen. In the Lagomorpha there is no anterior deep part. 3. The posterior belly of the digastric is well marked in the Myomorpha, in the Lagomorpha it is only present as a narrow tendon. 4. The transverse mandibular muscle is present in the Myomorpha, absent in the Lagomorpha. 5. The omo-hyoid is present in the Myomorpha, absent in the Lagomorpha. 6. The acromio-trachelian (levator claviculae) rises from the arch of the atlas in the Myomorpha. In the Lagomorpha it rises from the basioccipital and bifurcates below, one part going to the meta-cromion, the other to the clavicle and deltoid. 7. The scalenus anticus is sometimes present in the Myomorpha but absent in the Lagomorpha. 8. The scapulo-clavicularis is absent in the Myomorpha, except the Bathyerginae. It is present in the Lagomorpha. 9. The three parts of the deltoid are fused in the Myomorpha, separate in the Lagomorpha. 10. The biceps cubiti has two heads in the Myomorpha, one in the Lagomorpha. 11. Among the Myomorpha the rotator humeri is only present in the Cricetinae. In the Lagomorpha it is present in both rabbit and hare. 12. The pronator quadratus is present in the Myomorpha, absent in the Lagomorpha. 13. The clavo-cucullaris part of the trapezius is generally present in the Myomorpha, absent in the Lagomorpha. 14. The splenius colli is absent in the Myomorpha, present in the Lagomorpha. 15. The rectus abdominis frequently decussates with its fellow of the opposite side in the Myomorpha. In the Lagomorpha there is n o decussation and the lineae trstnsYersae are much better. marked. .o....\;:\..:.,.... v... •„: |