STRUCTURE OF BONE. 



587 



Fio. 301. 



lacunae of Reptiles, without a corresponding increase in breadth ; 

 and this is also seen in some Fishes, thoiSgh in general the lacunae 

 of the latter are remarkable for their angularity of form, and the 

 fewness of their radiations, — as shown in Fig. 301, which repre- 

 sents the lacunae and ca- 

 naliculi in the bony scale 

 of the Lepidosteus ("bony 

 pike" of the l^orth Ame- 

 rican lakes and rivers), 

 with which the bones of 

 its internal skeleton per- 

 fectly agree in structure. 

 The diniensions of the 

 lacunae in any bone do 

 not bear any relation to 

 the size of the animal to 

 which it belonged ; thus 

 there is little or no per- 

 ceptible difference between their size in the enormous extinct 

 Iguanodon, and in the smallest Lizard now inhabiting the earth. 

 But they bear a close relation to the size of the blood-corpuscles 

 in the several classes ; and this relation is particularly obvious 

 in the " perennibranchiate" Batrachia, the extraordinary size of 

 whose blood-corpuscles will be presently noticed (§ 414) : — 



Section of Ihe bony scale of Lepidosteus : — a, showing the 

 regular distribution of the lacunae and of the connecting 

 canaliculij 6, small portion more highly magnified. 



Proteus, 



Siren, 



Menopoma, 



Lepidosiren, 



Pterodactyle, 



Long Diameter. 



1-570 to 1-980 

 1-290 to 1-480 

 1-450 to 1-YOO 

 h315 to 1--494 



Short Diameter. 

 1-885 to 1-1200 

 1-540 to 1-975 

 1-1300 to 1-2100 

 1-980 to 1-2200 



1-445 to 1-1185 1-4000 to 1-5225' 



405. In preparing sections of bone, it is important to avoid the 

 penetration of the Canada balsam into the interior of the lacunae 

 and canaliculi ; since, when these are filled by it, they become 

 almost invisible. Hence it is preferable not to employ this ce- 

 ment at all, except, it may be, in the first instance ; but to rub 

 down the section beneath the finger, guarding its surface with a 

 slice of cork or a slip of guttapercha (§ 111) ; and to give it such 

 a polish, that it may be seen to advantage even when mounted 

 dry. As the polishing, however, occupies much time, the benefit 

 which is derived from covering the surfaces of the specimen with 

 Canada balsam may be obtained, without the injury resulting 

 from the penetration of the balsam into its interior, by adopting 

 the following method. A quantity of balsam proportioned to the 

 size of the specimen is to be spread upon a glass slip, and to be 



' See Prof. J. Quekett's Memoir on this subject, in tlie " Transact, of the Microsc. See." 

 Ser. 1, vol. ii ; and his rnore ample illustration of it in the " Illustrated Catalogue of the 

 Histological Collection in the Museum of the Roy. Coll. of Surgeons," vol. ii. 



