Plagiostomata of the Pacific. Pt. I. Fam. Heterodontidae / by N. de Miklouho-Maclay and William Macleay.
- Nicholas Miklouho-Maclay
- Date:
- [1878]
Licence: Public Domain Mark
Credit: Plagiostomata of the Pacific. Pt. I. Fam. Heterodontidae / by N. de Miklouho-Maclay and William Macleay. Source: Wellcome Collection.
Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.
19/34 page 321
![in the series of Elasmobranchii, induced me to regard the investi- gation of the dentition of the embryonic stages of that genus as a matter of high interest and importance. Unfortunately, I could procure no Heterodontus embryos, but this proved not to be an insuperable obstacle, as the examination in young specimens of as much as 225 mm. (8'9 in.)* *• in length of the form of the teeth, which differ very markedly from those of the adult, affords us a glimpse into the genealogical connection of this shark with the other Plagiostomata A glance at the teeth of a young E. Phillipi (PI. 24, fig. 14), magnified about five diameters, is sufficient to establish the great similarity between the dental armature of the young Eeterodontus and that of the Notidani##. This preparation (fig 14) shows us further that at this age (225 mm. in length) not more than seventeen series (i.e., vertical rows) are developed in the upper jaw, and thirteen in the lower. In both jaws only three horizontal rows of both series are to be seen, the others come into view after the mucous membrane of the palate has been dissected off. The teeth situated in the very front of the lower jaw have three almost similar pointed cusps, while those situated further back have five points. (Vide fig. 15, PI. 24).*** The teeth of the middle row are more or less symmetrical, and in the posterior (reserve) teeth of this row the central cusp is the largest, while the two outer take the form of inconspicuous tubercles. The teeth of the lateral rows are also longer, in pro- portion to their height, than those of the middle rows. On a closer inspection we see that the two anterior cusps of the lateral teeth are more perpendicular than the others, a feature which is met with in some fossil Notidanus teeth. (Vide Agassiz Poissons * Mr. Mfccleay believes that this specimen had only emerged from the egg one or two days. *• This circumstance gains greater significance, when we considor that the investiga- tion of the brain of the Heterodontus leads us to a similar conclusion in regard to the connections between those two genera. The brain of H. Phillipi stands very near the general fundamental form of the vertebrate central nervous system, and as such, resembles the brain of the Notidani, of the genera Acanthias and Scymmus. (Beitrage zur var gleichanden Neurology, I., p. 43.) “* The difference between the teeth of the young Heterodontus and that of the adult has already been noticed by Mtlller and Henle as follows:— •' Zahne, in der Mitte, klein und spits, aus drei bis fUnf von der Basis gegen die Spitzen ausseinandertretenden Zacken gebildet, von denen die mittlere am grossten ist, die bei alten Thieren abgesch- liffensindj (Mtlller und Henle, Systematische Beschreibung der Plagiostomen, 1841 Pag 70. [17]](https://iiif.wellcomecollection.org/image/b22367913_0019.jp2/full/800%2C/0/default.jpg)
