1866.] ON THE ANATOMY OF THE CRESTED AGOUTI. 393 



P. c). It corresponds very nearly to our description of the same 

 muscle in Hyrax*. It is also wonderfully strong in the Rodents 

 selected for comparison, most so perhaps in the Guinea-pig. 



The latissimus dorsi takes origin from the dorsal and lumbar ver- 

 tebrae, and is likewise attached by a fascia to the surface of the infra- 

 spinatus muscle. It has an insertion by tendon, as usual, in common 

 with the teres major (figs. 2 & 3, L. d.). It sends off a small dorso- 

 epi trochlear slip (figs. 2 & 3, D. e.) to the ulnar side of the olecra- 

 non. This last we noticed in the Guinea-pig, but not clearly in the 

 specimens of Rabbit and Hare. 



The trapezius is very extensive and elongated (fig. 3, Tra.). Mus- 

 cular fibres come from the spines of the fourth to the eleventh dorsal 

 vertebrae, covering the latissimus dorsi, and proceeding outwards and 

 forwards are partially inserted into about the middle of the spine of 

 the scapula. 



A strong tendinous fascia continues onwards, joining the almost 

 distinct anterior portion, which may be said to arise from the occiput 

 and ligamentum nuchae, to be inserted into the anterior edge of the 

 spine of the scapula and metacromion process, a slip of fibres pro- 

 ceeding down the side of the limb as far as the middle of the humerus. 

 In the neck the fibres join those of the levator claviculae. 



There is no characteristic difference in the Guinea-pig. 



In the Hare the nuchal portion is very thin, and the dorsal por- 

 tion goes as far backwards as the twelfth or thirteenth vertebra. 



In the Rabbit this muscle appears to join the latissimus dorsi 

 posteriorly. In neither of these three animals is the long humeral 

 slip so strongly developed as in the Agouti. 



Rhomboideus. There is no distinction between the rhomboideus 

 major, minor, and capitis ; but one continuous sheet of muscle arises 

 from the paramastoid process of the occiput, the median line of the 

 neck, and the dorsal vertebrae. Its insertion is into the vertebral 

 border of the scapula. 



Meckel says (loc. cit. p. 242), "Le Pore-epic et la Marmote parmi 

 les Rongeurs n'ont qu'un rhombo'ide, mais il y est tres-developpe, il 

 vient de 1' arcade de l'occipital," &c. 



In the Hare, Rabbit, and Guinea-pig we find a distinct rhomboi- 

 deus capitis muscle, which arises by delicate narrow fibres from the 

 occiput, and, broadening as it proceeds backwards and outwards, is 

 inserted into the anterior end of the vertebral border of the scapula. 



In them also the rhomboideus major and minor are interblended. 



The serratus magnus and the levator anguli scapula, indivisibly 

 united together, form another extensive layer of muscle. Origin : the 

 transverse processes of all the cervical vertebrae and the first eight 

 ribs. Insertion : the spinal border of the scapula beneath the rhom- 

 boideus. 



In the Guinea-pig, Rabbit, and Hare there is a line of separation 

 between the serratus magnus and levator anguli scapulae, opposite 

 the third rib ; the last portion has the greatest amount of attach- 

 ment to the scapula. 



* P. Z. S. 1865, p. 335. 



Proc. Zool. Soc— 1866, No. XXVI. 



