Proceedings of the general meetings for scientific business of the Zoological Society of London, 1896

Page 226

188 MR. F. G. PARSONS ON T H E [Jan. 14, 7. The claviculo-scapularis is absent in the Myomorpha, present in the Hystricomorpha. 8. In the Myomorpha the three parts of the deltoid lie close together. In the Hystricomorpha they are separated by distinct intervals. 9. The biceps cubiti has two heads in the Myomorpha. In the Hystricomorpha there may be one or two. 10. The Myomorpha seldom have the first part of the coraco-brachialis, in the Hystricomorpha it is often present. 11. The splenius colli is never found in the Myomorpha, in the Hystricomorpha it is sometimes seen. 12. The two parts of the biceps femoris are usually distinct in the Hystricomorpha. In the Myomorpha they are seldom separable. 13. In the Myomorpha the flexor tibialis and flexor fibularis do not usually join in the sole. In the Hystricomorpha they are always united. 14. In the Myomorpha the accessorius is absent or very ill-developed. In the Hystricomorpha it is present and well marked. Differences between the Myomorpha and the Sciuromorpha. 1. The three parts of the temporal muscle are more closely fused in the Myomorpha than in the Sciuromorpha. 2. A small part of the masseter passes through the infraorbital foramen in the Myomorpha. No part passes through in the Sciuromorpha. 3. The three parts of the deltoid are more closely fused in the Myomorpha than in the Sciuromorpha. 4. In the Myomorpha a rotator humeri is only found in the Cricetinae. In the Sciuromorpha it is always present. 5. In the Myomorpha the flexor sublimis digitorum sends no slip to the fifth digit. In the Sciuromorpha this slip is present. • 6. The supinator longus is absent in the Myomorpha, but is present in the Sciuromorpha except Castor1. 7. The extensor longus digitorum always sends a tendon to the fifth digit in the Sciuromorpha; this tendon is often absent in the Myomorpha. 8. The rectus abdominis often decussates at its origin with its fellow in the Myomorpha. There is no decussation in the Sciuro­morpha. 9. The quadratus femoris is triangular in the Myomorpha, quadrilateral in the Sciuromorpha. 10. The supracondylar slip of the semi-membranosus always rises from the tuber ischii and is closely connected to the adductors in the Sciuromorpha. In the Myomorpha it may rise from the tuber or caudal vertebrae and is distinct from the adductor mass. 1 Macalister describes an exceedingly feeble supinator longus in the Beaver (' Morphology of Vertebrate Animals,' p. 289).