138 MAMMALIA.— DENTITION OF MAMMALS. 



There are two in the European seas, viz., — the Great Rorqual (Bat. loops, Lin.), — superior in length to the com- 

 mon Whale, and shunned on account of its extreme ferocity, and the small quantity of its oil ; and the Small Ror- 

 qual {Bal. miisculiis, Lin.), which differs from the other [in its very inferior size, in its proportions, and number 

 of vertebrae. There is a third in the southern seas, and also a distinct fossil species. 



On proceeding to determine the fixed analog;ies of the teeth throug^hout the different groups of Mammalia, we 

 have arrived (since most of the foregoing pages were stereotyped) at the conclusion, that no placental mammalian 

 has more than three pairs of incisors, or three pairs of true or persistent molars, (normally,) in either jaw; all 

 seeming exceptions being reducible to this general proposition : whereas the Marsupials have normally four of 

 each, and some even five. By persistent molars, are intended those which are not preceded by milk-teeth. 



Following, then, the indications afforded by the structure of the molars, (which we conceive to furnish the most 

 available guide to sound classification,) we are next led to recognize two principal varieties of dentition among the 

 Placenfalia, to one or the other of which every observed modification may be definitively referred. These two 

 varieties are characteristic of a great zoophagous type and a great plti/tophagous type. 



Where exceptions occur in the former instance, the amylaceous parts of vegetables, as fruits, seeds, and fari- 

 naceous bulbs or roots, are almost exclusively resorted to; and animal products are preferred to the composition 

 of the recent carcass in those few exceptive cases which, in a trivial degree, aflect the latter generalization. 



The zoophagous type of dentition is obviously of a higher grade than the other, and the animals in which it 

 occurs require more nutritious aliment. 



Throughout the zoophagous division, the molars are compact In texture, and the enamel never dips into their 

 substance ; the basal growth of the teeth (except the pseudo-incisive canines only, in the very singular genus 

 Chejromtjs,) ceases upon the latter attaining their required size ; in consequence of which they gradually wear 

 down by attrition, till in aged animals they are not unfrequently reduced to stumps. 



In the phytophagous division, the molars are much less compact, and the enamel generally dips into 

 their substance in various ways ; the teeth are commonly furnished with persistent formative pulps, which 

 deposit fresh substance at their base as their crowns wear away, so that they continue permanently growing. The 

 exceptions that occur to this general definition do not intrinsically affect the distinctness of the present group 

 from the other, and are easily understood, so that a transverse section of a molar (known to be that of a placental 

 animal) will suffice in every instance for the determination to which it belongs. 



These two great divisions somewhat analogously subdivide each into two sections, which differ considerably in 

 the general details of their organization, and most commonly in the structure of the teeth. They may be regarded 

 as normal and abnormal sections. 



In the normal sections of the zoophagous and phytophagous grand divisions of Pla-centalia, the four sorts of 

 teeth — incisors, canines, renewed and persistent molars — are generally present, or at least three sorts of them, 

 *ach characterized by a particular form and structure different from the rest. In the abnonnal sections, the teeth 

 are commonly much more numerous, and alike in structure, and consist principally or even wholly of false 

 molars ; all of them are without exception single-rooted. 



We might consider these four sections as Orders, and denominate them as follow. 



A. Zoophagous type. 



1. Typodontia. Normal: comprehending the -Bfj/iawn, QKarfz-umana, and Ca/viojiier* of Cuvier. 



2. Jsodontia. Abnormal : consisting of the Cetacea of Cuvier, divested of the herbivorous subdivision. 



B. Phytophagous type. 



3. Diplodontia. Normal: comprising the Pachydermata, Cetacea herhivora, Rodentia, and Rnminantia of 

 the same naturalist. 



4. Aplodontia. Abnormal: corresponding to the £(ie7(/a^a of Cuvier, divested of the J/ono/j-ema/ff. 



These together constitute the «or>«a/ or placental subclass of Mammalia; and i\\e abnormal or ovo-viviparous 

 subclass might range in two orders only, viz. : 



5. Ileterodontia. tiormal: or the Marsupiata: a.nd 

 C. Pseudodontia. Abnormal : or the Monotremata. 



The Typodontia primarily subdivide into the Primates and Ferte of Linnaeus, or Secundates, as the latter has 

 recently been termed by De Blainville. 



The Primates are characterized by the external distinctions popularly known, and also, it may be added, by their 

 hair being of one sort only, having never any softer felt beneath it.* They separate into Cheiropoda and Cheiroptera. 



The Cheiropoda comprise the Bimana and Quadrumana of Cuvier, but not the marsupial handed animals, in- 

 cluded under this name by Mr. Ogilby. Tlicy liave never more than four incisors in either jaw, invariably pos- 

 sess a coecum, have no os penis, and are born with the eyes open. They subdivide into Anthropida and Lemuria. 



The Anthropida are characterized by the general form of the head, the complete separation of the orbits from 

 the temporal fossa by a bony partition, by having the inci-sors broad and contiguous, and vertical, or nearly so, 

 in both jaws, by their anthropoid molars, &c. Their teeth form an even series, the continuity of which is only 

 broken by the interspace required for the reception of the opposite canine ; and in Man only, where the canines 

 arc not lengthened beyond the other teeth, even this vacuity does not occur. They fall into the Catarrhini and 

 Platyrrhint of Geoffroy, according to the number oi false molars; and the circumstance of their being respectively 

 peculiar to the Old and New Worlds, affords a presumptive argument that the human genus, which pertains 

 strictly to the former, is not indigenous to America. 



• Wc were deceived by certain Kppcaraiices in stating that exceptions to this rule existed, at pp. 45 48. 



