G08 R. J. HARVEY GIBSON ON THE 



number — two anterior, two posterior, and two lateral. The anterior cartilages 

 are the largest ; they are pointed and slightly curved upwards in front, and are 

 arranged like the legs of the letter V, with the apex pointing towards the mouth 

 (PI. CLIII. fig. 66). At the bases of the legs lie the posterior cartilages, and 

 closely attached to them. The posterior cartilages are square blocks with 

 corners rounded off. The lateral cartilages lie alongside the anterior cartilages, 

 and towards their anterior ends. They are triangular in shape, having the base 

 of the triangle anterior. These various cartilages are bound to one another (a) 

 by connnective tissue, and (b) by muscles, (a) Distinct bands of connective 

 tissue bind the posterior cartilages to the anterior, and also the lateral to the 

 anterior, (b) There are also a number of muscles which connect the various 

 cartilages to each other ; a band uniting the anterior and lateral cartilages on 

 either side, dorsally ; two bands or sheets uniting the two anterior cartilages, 

 ventrally ; the upper of these being the broader and larger, and being separated 

 from the under narrower band by two bands of muscle passing from the infra- 

 radular membrane to the base of the posterior cartilage on either side ; and, 

 lastly, a band uniting the anterior and lateral cartilages on either side, ventrally. 

 All these muscles may be termed intrinsic. There are, however, in addition 

 several extrinsic muscles connecting the buccal mass with the neck wall. 

 Firstly, two broad plates attached posteriorly, one on either side to the posterior 

 cartilage, anteriorly to the floor of the neck cavity. These may be termed the 

 ventral protractor fibres (PI. CL. fig. 17, v.pi\). Also attached to the posterior 

 cartilage on either side is a lateral protractor, which is attached anteriorly to 

 the roof of the neck cavity. Finally, attached laterally to the anterior cartilage, 

 on either side, is a vertical band of muscle, attached at its upper end to the 

 roof of the neck cavity. Many delicate muscular fibres also pass from the 

 pharynx to the walls of the neck cavity. 



Returning now to the pharynx, it is found, as already stated, to be more or 

 less divided externally by two longitudinal furrows into three parts, a central 

 and two lateral. These several parts are in complete communication with each 

 other, the division being rather apparent than real. Anteriorly the wall of the 

 pharynx is thickened by the development of two oval yellowish-brown masses, 

 one on either of the lateral divisions. Into these masses the four very evident 

 salivary ducts open, two into either mass (PI. CLIII. fig. 61). The ducts are long 

 isolated, slightly twisted, yellowish-brown tubes which run from thence back- 

 wards, the two inner lying in the furrows of the pharynx, but easily detachable 

 therefrom, the two outer running alongside the odontophore. The two inner 

 enter the salivary glands about the middle ; the two outer are attached to the 

 glands at their extreme edges (PL CLIII. fig. 61). The glands themselves vary 

 somewhat in size and colour. They are usually large orange-coloured masses 

 closely united together, lying over the shoulders, beneath the pericardium on one 



