286 PEOr. W. B. BENHAM ON THE [-^Pl'* 2, 



separable sheets, a right and a left ; these are inserted partly in the 

 " cornu " of the cricoid, and partly in the five or six uppermost 

 tracheal rings on each side. 



This longitudinal muscle is, topographically, a " tkyro-cricoid." 



(b) Below the " thyro-cricoid " is a thick layer of muscle 

 (I inch in thickness), dispersed transversely for the most part, but 

 some fibres pass entirely round the sublaryngeal sac (PI. XXV. 

 fig. la, n). The transverse muscles are inserted at each end to 

 the inner (i. e. doi^sal) face of the cricoid cornu. 



(c) This transverse, or inter-cricoid, muscle is not distinctly 

 separated from a series of muscle-fibres (r) that also are related 

 to the sublaryngeal sac. These fibres pass from the antero-ventral 

 margin of the cricoid, obliquely forwards to their origin in the 

 inner face of the body of the thyroid. The more ventral fibres of 

 this nuiscle, becoming more and more oblique with regard to the 

 sagittal plane, ultimately become transverse, and I was unable to 

 separate this sheet from the " transverse muscles " just described, 

 but they are quite distinct from the longitudinal thyro- 

 cricoid s. 



This sheet of " accessory crico-thyroids " (r) forms the side-walls 

 of the anterior part of the sublaryngeal pouch. 



Murie (1871) has suggested that the muscular wall of this pouch 

 is derived from the thyro-arytenoid muscle ; in this he is supported 

 by Dubois (1886), who sees also a representative of the lateral 

 crico-arytenoid in part of the musculature. In this latter view 

 I am inclined to concur, so far as my observations on Baltenoptera 

 go ; for the sheet of muscle labelled "r " in the figures appeared 

 to be quite continuous with that portion of the crico-arytenoid 

 which passes round to the side of the cricoid, and it was only 

 separable by careful dissection. Now this muscle (r) is continuous 

 with "71," which forms the inner muscular coat of the sublaryngeal 

 pouch, so that the representative of the " lateral crico-arytenoid " 

 is here in the Mystacocetes of enormous size. 



In discussing the myology of the human larynx, Kanthack 

 (1892) has, by the use of microscopic sections, confirmed the view 

 held by Disse and Fiirbringer that the " lateral crico-arytenoid " is 

 only part of — " a second head of " — the thyro-arytenoid, some of 

 the descending fibres of which " blend with the lateral crico-ary- 

 tenoid, and come into close connection with the crico-thyroid." 

 I think my observations confirm this view. 



3. The thyro-ejoiglottidean muscle {T.ep.) is also a conspicuous 

 constituent in the ventral region of the larynx ; it arises from the 

 inner face of the lateral region of the body of the thyroid, and 

 passes forwards into the mass of muscle that forms, with the 

 cartilage, the "epiglottis." The fibres of this muscle are not 

 distinctly marked off from that part of the aryteno-epiglottid 

 muscle lying in front of the thyroid. 



4. Erom the dorsal surface (PI. XXV. fig. 2) two muscles are 

 seen: the paired crico-arytenoids (O.ar.) and the inter-arytenoid 

 {I.ar.). 



