302 MR PHILIP J. WHITE ON THE 



Hyoidgill rays. — These are either simple or branching rods of cartilage which project 

 backwards and outwards from the hinder parts of the hyo-mandibular and cerato-hyal 

 cartilages. As a rule, there are about eleven rays on each side, the majority of the rays 

 springing from the cerato-hyal. The ray on either side of the joint, formed by the hyo- 

 mandibular and cerato-hyal cartilages, is stouter than the others. 



Extra-branchials. — There are two of these on each side, an upper and a lower, and 

 they form the first of the series of extra-branchial cartilages (PI. I. Figs. 1 and 2, Ev, Ev'). 

 None of the hyoid gill rays touch the upper extra-branchials of this arch, but several are 

 in contact with each of the lower extra-branchials. 



The Mandibular Arch. 



This consists of the palato-pterygoid and mandibular cartilages which constitute the 

 upper and lower jaws (PL I. Figs. 1 and 2, PI. II. Fig. l). 



The Upper Jaw. — This is formed by the two palato-pterygoid cartilages (Ppt), one 

 on each side of the middle line. The anterior extremities of these cartilages are bound 

 together by ligament, but they do not touch one another, while their posterior ends are 

 widely separated. Each cartilage has a direction from before backwards and outwards. 

 Immediately external to the maxillary symphysis there is a slight elevation of the carti- 

 lage, to the outer side of which lies the narrowest portion of the palato-quadrate. 

 The elevation just noted is much more marked in Scymnus. Beyond its narrowest 

 portion the palato-pterygoid becomes suddenly wide, and continues so to its posterior 

 extremity. At the commencement of the wide portion a large somewhat conical process, 

 the palato-basal process (Pp), is placed on the upper part of the jaw. In the recent state 

 this process rests on the palato-basal depression (PI. I. Fig. 4, Fd) of the skull. At the 

 inner part of the base of the process there is a deep hollow, above which there is a con- 

 siderable projection. Each palato-basal process is surmounted by a nodule of cartilage (n). 

 The upper edge of the palato-pterygoid behind the palato-basal process becomes much 

 everted, and the upper part of the inner surface of the cartilage, especially towards its 

 hinder part, looks upwards and backwards. The outer surface of the palato-pterygoid 

 in its posterior two-thirds presents a concavity. At the posterior extremity of the cartilage 

 there is a faceted surface internally and an articular process externally, both of which 

 are for articulating with the lower jaw. 



Teeth are found on the lower and inner part of the anterior two-thirds of the palato- 

 pterygoid cartilage. The younger teeth lie in a depression which is bounded above by a 

 ridge. 



The Pre-spiracular Cartilages (PI. I. Fig. 1, Ps). — These are two small flattened 

 cartilages which rest on the surfaces of the palato-pterygoid cartilages, which are directed 

 upwards and backwards. The cartilages are longer than they are broad, and have a direc- 

 tion upwards, forwards, and outwards. 



TJie Lower Jaw. — The lower, like the upper, jaw consists of two cartilages, the man- 

 dibular cartilages (Mm), one on either side of the mesial plane, and are bound together in 





