292 PEOF. W. B, BENHAM ON THE [Apr. 2, 



The region that represents tlie " processus muscularis " of 

 Balcenoptera is here a slight, nearly circular, convex prominence, 

 not at all well marked. The internal face of the entire cartilage 

 is smooth. 



The length of the arytenoid is 5| inches ; its greatest breadth 

 is 1| inches ; while its upper moiety is only five-eighths of an 

 inch 3)Ci*oss 



The exnglottid cartilage (PI. XXVI. fig. 13, PL XXVII. fig. 14) 

 has the usual trough-like character ; it is, in contrast with that of 

 Balcenopteni, very massive, being 6 inches in length, and its greatest 

 breadth is 1| inches. Seen in side view, it is club-shaped in out- 

 line ; the upper, narrower region being somewhat flattened from 

 side to side, while the broader posterior region is much compressed ; 

 at the junction of these two regions the hyo-epiglottid muscle is 

 inserted. This lower region is rounded posteriorly, where it abuts 

 against the thyroid plates. 



The lateral surfaces are here somewhat excavated, serving for 

 the attachment of muscles. These siu-faces meet in a relatively 

 sharp ventral edge. Tlie upper end of the cartilage becomes quite 

 thin, and the extreme upper margin is recurved. 



The posterior or internal surface is grooved ; this groove at its 

 commencement is shallow and wide, but further down becomes 

 deeper and narrower. Rising from the floor of the groove in 

 the upper half is a ridge, which fades away posteriorly ; thus a 

 transverse section near the upper region is W-shaped, while lower 

 down it is V-shaped. 



The broad base of the epiglottid cartilage is capped by two 

 small cartilages : one is patelliform, measuring | X | inch, and is 

 thrust between the two thyi-oid plates so as to be visible when 

 the ventral margins of these are parted (PI. XXV. fig. 4) ; the 

 second is smaller, oval, and nodular in form, situated dorsal of the 

 first ; it measures three-eighths of an inch long, and is closely 

 related to the ventral edge of the right thyroid plate, connected to it 

 by fibrous tissue. It is situated at the origin of the thyro-arytenoid 

 muscle of the right side, and rests against a small hard prominence 

 on the inner surface of the ventral edge of the left thyroid plate. 

 Each of these two subepiglottid cartilages is separated from the 

 epiglottis by the thickened layer of fibrous tissue. It is possible 

 that they represent the " lobulse " of the 4th and 5th visceral arch, 

 one of which persists in Echidna. I saw no representative of the 

 process (marked c in Howes's figures) passing inwards from the 

 base of the epiglottis towards the base of the arytenoid, to which it 

 is connected by fibrous tissue. 



Muscles of the Larynx. 



The outer surface of each thyroid plate serves for the attachment 

 of three muscles (PI. XXVI. fig. 6). 



1. The thi/ro-hyoidmnsc\e{T.h.) is attached over the whole breadth 

 of the anterior region of the plate, partly to the thickened edge. 



