904 PROFESSOR W. C. M'INTOSH AND MR E. E. PRINCE ON 



preparations it appears that this tissue is formed in the perichondrial cellular coat ; indeed, 

 near the symphysis the very small deeply stained cells clearly intervene between the 

 hyaline deposit and the cartilage itself. The hyaline matter, moreover, does not in 

 transverse section exhibit the same cylindrical form as the mandibular bar ; for, though 

 rounded on the outer side, it rises into a blade-like ridge on the inner side, while above 

 its surface is flattened. 



The maxilla in Salmo presents a different appearance from most of the other cartilages, 

 since the cells are indistinct, the markings resembling irregular waves, except at the 

 anterior and posterior ends. Between the sixth and seventh weeks the dentary region of 

 the mandible shows many teeth, arranged in several rows, the anterior being curved, the 

 posterior more or less straight. About thirty teeth occur on the premaxillae and maxillae. 

 The mucous membrane is raised into papilliform elevations, the summit of each bearing 

 a tooth. The premaxillary teeth are the largest and strongest. The otoliths are at 

 this stage the only hard and dense structures in the cephalic region, and they are some- 

 what spherical, and present the usual radial striations. The posterior otolith in each 

 auditory sac is irregular, and shows longitudinal markings and interrupted streaks. The 

 cells of the cranial cartilages are, on the whole, more regular and distinct than those of 

 other parts. 



Hyoid Arch. — The embryos of the wolf-fish which issued on 17th January presented 

 a well-developed hyoid arch. The glosso-hyal region has anteriorly a large cushion of 

 mucous tissue. Three cartilaginous elements form a rounded arch within the latter 

 (PI. XXV. fig. 1), viz., a median (glosso-hyal) and two lateral (hypo-hyal). The cerato- 

 hyals abut on the hypo-hyals. In all these the cartilage-cells are smaller than in the salmon. 

 The cerato-hyals are considerably less than in the salmon, and, indeed, the same may be 

 said of the cartilaginous elements in general, and especially of the glosso-hyal. Four 

 branchial arches succeed the former, and bear simple though highly glandular papillae 

 (PI. XXV. fig. 2). The fifth arch is visible in a specimen on 20th April, as a bar on 

 each side in front of the pericardial chamber, and teeth are readily distinguishable on 

 1st May. The double rows of branchial pinnae present deep crenations along the sides in 

 April, and these form long papillae towards the end of the latter month and in May, so that 

 each process is feather-like. Hyaline ossific tissue now appears as a superficial coating 

 upon the surface of the branchial cartilages. On 21st May the cerato-hyal and other 

 cartilages of this region are bordered with a firm layer of the same tissue. The brittle- 

 ness of the branchial arches externally shows that this development has made consider- 

 able progress, and the ossific investment is still more marked a month later (20th June), 

 when it was difficult to make good sections, on account of the brittle character of the 

 skeletal bars, or rather of the hyaline ossific tissue clothing them. The branchial 

 papillae at this latter date are richly pinnate. 



The hyoid bar may, as in the gurnard, T \ inch in length, rapidly lose the form of 

 a simple rod, and while the mandible is rudely elliptical, the hyoid becomes bilobate in 

 transverse section, from the presence of deep grooves, and shows two prominent outer 



