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Show 1866.] ON THE ANATOMY OF THE CRESTED AGOUTI. 389 The lesser sciatic nerve is comparatively large, and is given off from the sacral plexus and great sciatic beneath the pyriform muscle. It lies upon the tuberosity of the ischium, and separates into several branches, which supply the conjoined gluteus maximus and biceps, the semitendinosus and semimembranosus, besides several other muscles. MUSCULAR SYSTEM. The anatomical structure of the genus Dasyprocta, in so far as the muscular system is concerned, has hitherto only been described in a somewhat fragmentary manner, principally by Meckel. Moreover, as the comparative relation of the myology in the Rodentia is interesting, we have thought this portion of the record of our dissection of D. cristata might be useful as helping to form a groundwork for further investigations with regard to that group ; for which purpose we have more particularly compared it with dissections made by us of the Guinea-pig, Hare, and Rabbit, availing ourselves at the same time of the labours of other observers on certain species of the order. W e may remark en passant that the flesh of the body of the Crested Agouti has a resemblance to that of the Common Hare, both in colour and in the absence of interstitial fat. Muscles of the Head and Neck. The temporal, compared with some of the muscles of mastication, is small, as it is in most of the Rodents. Its origin and insertion present nothing remarkable, excepting in its perpendicular pulley-like position and action round the posterior base of the zygomatic process. In the Guinea-pig it appears to be single and like the above. In the Hare this muscle is also feeble, but somewhat divided into two bellies, as Meckel* has stated. Masseter. This muscle in the Crested Agouti, as in many of the Rodents, is composed of more than one layer. W e found it divided into three distinct portions, somewhat in the manner described in the notes to the French translation of Meckelf. The first portion (jugo-maxillien) is the largest and most superficial. It arises from the whole length of the zygomatic arch, as far forwards as opposite the first molar tooth ; and it is inserted into the outer surface or ridge and lower margin of the mandible, some of the fibres turning round and being fixed into the inner face of that bone. The anterior border of this portion has a very strong superficial tendon. The second, smaller portion (mandibulaire) lies beneath the first, and is a muscular slip, also stretching from the zygomatic arch (its anterior end) to the mandible (its outer surface). * Anat. Comp. traduit par MM. Eiester et Alph. Sanson, Paris, 1829-30, vol. viii. p. 577. t JJOC. cit. p. 580 (footnote). At p. 328 in the same volume it is noticed that in its complete state the masseter is divisible into three muscles, viz. the jugo-maxillien, the mandibulaire, and the mandibulo-maxillien. |