504 MK. N. A. MACKINTOSH ON THE CflON DllOOIlANIDM 



paired rods, ending freely at both ends and lying just below the 

 apex of the notochord and behind the forebrain. There is a 

 marked cranial flexure. At present there is no sign of the para- 

 chordals. 



The visccrnl skeleton is represented by a relatively extensive 

 but barely differentiated mnss of procartilage. In this it is 

 possible to distinguish on each side an element running down- 

 wards from the auditory vesicle. This eleinent ultimately gives 

 rise to the jaw suspension apparatus. At the foot of it the 

 procartilage runs forwards for a short distance indicating the 

 position in which Meckel's cartilage is to be laid down. This 

 cartilage appears later as a condensation on each side which grows 

 fonVards as the cranial flexure is eased and the mouth moves 

 forwards. At the present stage the mouth has not appeared. 

 The rest of the mass of procartilage extends upwards and back- 

 wards and constitutes the rudiments of the branchial bars. 



b. Stage 2. The 4*5 mm. larva. 



The trabecula9 have at this stage lengthened considerably 

 (text-fig. 3) and form a roof to the mouth, which has now made 

 its appearance. The parachordals are now established and are 

 continuous with the trabeculae, but where they form the floor of 

 the auditory capsule they are in a procartilaginous condition. 

 They cannot, however, be distinguished as anterior and posterior 

 plates as in the case of Salmo, Gasterosteus, etc. The trabeculse 

 are closely approximated along the whole of their length and end 

 freely anteriorly, though there is at their extremity a condensation 

 of connective tissue representing the ethmoid plate. The noto- 

 chord reaches well forward and turns down under the rudiment 

 lof the infundibulum. 



In the visceral skeleton Meckel's cartilage lias made its appear- 

 ance, its two components being joined anteriorly by a tract of 

 procartilage. A substantial bar of cartilage articulates with the 

 lower jaw near its posterior end and with the lower surface of thti 

 auditory capsule. This element, which appears to be a piece of 

 continuous cartilage, later gives rise to the hyomandibular, 

 symplectic, and quadrate cartilages. Pouchet (1878) employed the 

 term " primordial temporal " to a somewhat similar element which 

 he found in certain forms. As " temporal " is now obsolete 

 as an alternative name for the hyomandibular, and as I am 

 unaware of any name at present in use which could rightly be 

 applied to the bar which, in Sebastes, joins the lower jaw to the 

 auditory capsule, I propose for convenience to call it the temporal 

 cartilage. From the posterior side of this temporal cartilage a 

 branch is given off which turns inwards and forwards as the 

 ceratohyal to join the anterior end of a mass of cartilage from 

 which the branchial bars are beginning to be differentiated. The 

 point at which the ceratohyal branches off is composed of rather 

 immature cartilage which later becomes more compact and forms 

 the stylohyal. 



