| OCR Text |
Show 294 MR. F. G. PARSONS ON THE [Mar. 20, except in Ceredon, in which a small adductor secundi digiti was found, but no adductor minimi digiti. General Summary. The amount of facts at my disposal does not, of course, justify anything like an attempt at a definite and complete summary of the muscles of the Hystricomorpha and Sciuromorpha. The following generalizations are merely suggested for future investigation. A. Differences between the Hystricomorpha and Sciuromorpha. 1. In the Hystricomorpha the anterior deep part of the masseter passes through the infraorbital foramen. In the Sciuromorpha it does not. 2. In the Hystricomorpha, with the exception of the Dipodidae, the digastric has no complete division into two bellies, and the muscles of opposite sides do not communicate. In the Sciuromorpha, as well as in the Dipodidae, a tendon completely divides tbe two bellies, and the muscles are connected across the middle line by a tendinous arcade. 3. The transverse mandibular muscle is absent in the Hystricomorpha, with the exception of the Dipodidae. It is present in the Sciuromorpha, with the exception of Castor. 4. The genio-hyoid muscles of opposite sides coalesce posteriorly iu the Sciuromorpha, but not in the Hystricomorpha. 5. The omo-hyoid is present or absent in the Hystricomorpha. It is always present in the Sciuromorpha. 6. The levator claviculae rises either from the atlas or the basioccipital in the Hystricomorpha. Always from the atlas in the Sciuromorpha. 7. The scalenus anticus is present in the Hystricomorpha, except in the Hystricidae. It is absent in the Sciuromorpha. 8. The trapezius is often divided into an anterior and posterior part in the Hystricomorpha. Never in the Sciuromorpha. 9. The sterno-scapular muscle is composed of the subclavius and tbe scapulo-clavicularis in the Hystricomorpha. In the Sciuromorpha, as well as in the Dipodidae, only the subclavius is present. 10. The first part of the coraco-brachialis (rotator humeri) is always present in the Sciuromorpha. In the Hystricomorpha it is present or absent. 11. The pronator quadratus is always attached to more than a third of the bones of the forearm in the Hystricomorpha. In the Sciuromorpha it is attached to a third. 12. The supinator longus is present in all the Sciuromorpha except Castor. It is absent in the Hystricomorpha except in Erethizon and the Dipodidae. 13. The scansorius is always wanting in the Sciuromorpha. It is often distinct in the Hystricomorpha. 14. The quadratus femoris usually has a tendinous insertion in the Hystricomorpha. It is fleshy in the Sciuromorpha. |
