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. More- 

 over, as the comparative relation of the myology in the Rodentia is 

 interesting, we have thought this portion of the record of our dis- 

 section of D. cristata might be useful as helping to form a ground- 

 work 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. 



We 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. We found it divided 

 into three distinct portions, somewhat in the manner described in 

 the notes to the French translation of Meckel"f . 



The first portion (jugo-maxillien) is the largest and most super- 

 ficial. 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. Riester et Alph. Sanson, Paris, 1829-30, 

 vol. viii. p. 577. 



t Loc. 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-niaxillien. 



