246 



NA TURE 



Yjfan. 25, 1872 



from the rest by the absence of middle incisor teeth, the 

 next four (4, 5, 6, 7) being reputed nondeciduate, the 8th, 

 9th, and loth presenting a zonary placenta, and the re- 

 maining orders a discoidal placenta. 



It was not to be expected that Professor Huxley 

 should have here departed from the placental classifica- 

 tion for which he has elsewhere shown so much favour. 



Fig. I.— The head o^a fcetal Lamb dissected so as to show Meckel's carti- 

 lage, .1/ ; the malleus, m ; the incus, i ; the tympanic, Ty ; the hyoid, // ; 

 the squamosal, i"^ : pterygoid,/';'; palatine,//; lachrymal,/^ ; prema.xilla, 

 pmx; nasal sac, N ; Eustachian tube. En. 



But however important the distinctions established upon 

 that basis may be in themselves, it may fairly be doubted 

 how far characters derived from parts which do not belong 

 to the permanent organisation of the adult animal, the 

 application of which is not yet fully known in one or two 

 orders, and in which, too, there is much of a transitional 

 nature, are preferable to signs of a more marked and 

 easily observable kind deducible from other parts of the 

 organisation. 



In the description of structure all these orders are 

 referred to ; but in several of them particular familiar ani- 



Fig. 2. — Diagram of the skeleton of the first and second visceral arche 



Lizard (A), a Mammal (B), and an Osseous Fish (C). 

 The skeleton of the first visceral arch is shaded, that of the second i 



nearly unshaded. /. First visceral arch. J/cA- Meskel's cartilage. Art. 



Articulare. Qii. Quadratum. M/'t. Metapterygoid ; iM. iMalleus ; f.g.. 



Processus gracilis. //. Second visceral arch. ,Hy. Hyoidean cornu. 



St. H Stylohyal. 5'. Stapedius. Stp. Stapes. S. Stf. Supra stapedial. 



//J/. Hyomandibnlar. The arrow indicates the first visceral cleft. /V. 



The periotic capsule. Pig. The pterygoid. 



mals are happily selected for the fuller illustration of the 

 more important system"^ ; as for exampl?, the horse, pig, 

 dog. rabbit, hedgehog, seal, ox, porpoise : thus suggesing 

 to the student the means by which a more practical and 



left 



thorough knowledge of the organisation may be obtained 

 by actual observation, than by the mere description of 

 varieties in a wider series of animals less within his reach. 

 In regard to the order to be followed in so extensive a 

 range of description as the comparative anatomy of 

 any large tribe of animals involves, it may be re- 

 marked that, however interesting in a physiological point 



Fig. 3. — Diagrammatic horizontal section of a Vertebrate Brain. The follow- 

 ing letters serve for botli this figure and Fig. 4 : — I^Ib, Mid-brain. What 

 lies in front of this is the fore-brain, and what lies behind, the hind-brain. 

 L.t. the lamina terminalis ; Otf, the olfactory lobes; //«(/. the hemi- 

 spheres ; Th.E, the thalamencephalon ; Pn. the pineal gland ; Py, the 

 pituitary body; F.M, the foramen of Munro: CS, the corpus striatum; 

 Th, the optic thalamus : CQ, the corpora quadrigemina : CC, the 

 crura cerebri ; C/>, the cerebellum: Pf, the pons varolii: MO. the 

 medulla oblongata ; / olfactorii ; //. optici ; ///. point of exit from the 

 brain of the motores oculorum ; 11'. of the pathetici; F7, of the abdu- 

 centes : V-XIl, origins ^of the other cerebral nerves. 1, olfactory ven- 

 tricle : 2, lateral ventricle ; 3, third ventricle ; 4, fourth ventricle : -f, iicr 

 a tertio ad qiiartum ventricithtni. 



of view may be the description of the variations of form 

 and structure in the different organs taken separately in 

 the whole series of animals, the results of this mode of 

 teaching and study are inferior to those obtainable from 

 the method of description of the whole organisation in 

 successive groups or individual animals, as regards pro- 



-A longitudinal and 

 before. The la 

 black line bet:vecn FM and 3 



Vertebrate Brain. The 

 presented by the strong 



gress in morphological attainments, the determination of 

 zoological affinities, and their application to the solution of 

 the great biological problems of the day. 



The latter p irt of this chapter treats of the Primates, 

 which are divided into — i, the Lemurids, 2, the Simiadas, 

 and 3, the Anthropidaa. The Simiada: are thrown into 

 three group?, viz., I, Arctopithecini, or marmosets ; 2, Pla- 

 lyrrhini, or American monkeys ; and 3, Catan-hini, or 

 monkeys of the Old World, including two sub-groups, 



