390 MR. ST. GEORGE MIVART AND DR. J. MURIE [June 26, 



The third portion (mandibulo-maxillien of notes to Meckel) forms 

 a flat muscular arch, with an anterior peak, attached to the side of 

 the superior maxillary hone and parti)- beneath the orbit. The fibres 

 converge and end in a very powerful glistening tendon, which is in- 

 serted into the anterior end of the external ridge of the mandible 

 nearly opposite the first molar. 



With regard to the action of this muscle, our observation corrobo- 

 rates Meckel's aunotators, who state that the first portion produces 

 both an antero-posterior and up and down movement of the man- 

 dible, while the third portion, from its pulley-like position and attach- 

 ments, only raises the lower jaw. 



Mr. Waterhouse* particularly calls attention to the constancy of 

 the double arrangement of the masseter in the Hystricidce, and 

 figures that of the Agouti and others ; but he does not speak of the 

 other, smaller slip mentioned in Meckel's work. 



The buccinator is very largely developed, and extends from the 

 mandible to the maxilla. 



It is also large in the Guinea-pig. 



The digastric muscle is large, normal in origin and insertion, and 

 has a median tendon. 



It is the same in the Guinea-pig, where it lies very deeply. 



In the Hare this muscle is very remarkable, as it possesses no pos- 

 terior fleshy belly, but its hinder half is merely a long tendon. 



Cuvierf remarks that there is but one belly in the digastric of the 

 Rabbit. 



The sterno-mastoid arises from the outer side of the elongated 

 manubrium, immediately beneath the third part of the pectoralis 

 major (p. 396. fig. 2, St. m). Passing forwards and upwards £ it is 

 inserted by a strong tendon into the anterior aspect of the parocci- 

 pital process. 



The cleido-mastoid is smaller than the preceding, and arises from 

 about the middle of the clavicle (p. 401 . fig. 3, CI. m) §, being inserted 

 broadly into the paramastoid process behind and beneath the sterno- 

 mastoid. 



In the Rabbit and Hare the sterno-cleido-mastoid is also separated 

 into two distinct portions as in I), cristata. In the Guinea-pig, ac- 

 cording to Meckel ||, with whom we agree, the cleido-mastoid, or 

 posterior half, differs from the above in being the larger portion of the 

 two. Moreover he says, " elle se confond tout-a-fait avec le deltoide 

 dans sa partie inferieure ;" but what he takes as part of the deltoid, 

 we are inclined to consider a clavicular part of the pectoralis major. 



The sterno-hyoid and stemo-thyroid muscles arise in common 



* Nat. Hist. Mamm. vol. ii. p. 151 and pi. Qa. f. 1-4. 



t Lemons d'Anat. Comp. tome iv. premiere partie, p. 93. 



J It must be understood that in our use of the terms " forwards," " upwards," 

 " anterior," " inferior," &c., we describe the animal as in the horizontal position 

 of a quadruped : therefore what in human anatomy would be spoken of as 

 " superior" is here " anterior;" and in the same manner " posterior" becomes 

 " superior," and vice versa. 



§ Meckel, Anat. Comp. vol. vi. p. 104. 



|| Loc. cit. p. 164. 



