796 DIRECTIONS FOE LABORATORY WORK 



a dentinal tubule. Sketch l.p. (225) a portion of the area of contact 

 between root of tooth and alveolar process. Note: a, alveolar bone; b, 

 periosteum and pericementum ; c, circular dental ligament; d, epithelial 

 remnants of dental lamina; e, fibers of Sharpey; f, cementum cells. 



(2) Study l.p. an axial ground section of tooth. Note in the enamel, 

 the contour lines of Eetzius and the prism stripes of Schreger; in the 

 dentin, the dentinal tubules, the contour lines of Owen, and the incre- 

 mental lines of Schreger. Make h.p. sketches (226) of small areas of 

 the enamel showing the prism bundles cut transversely and longitudi- 

 nally; also (227) of small areas of the dentin' showing the tubules cut 

 transversely and longitudinally. Sketch also (228) a small area of the 

 cementum; and (229) of the granular layer of Tomes in the region of 

 the neck of the tooth. Describe the complete form, structure, content 

 and significance of the dentinal tubules. 



(3) Sketch (230) several successive early stages in the development 

 of the deciduous teeth in a stained vertical section of the jaw of some 

 mammalian fetus "(e.g., of 25 mm. pig embryo). Note: a, labiodental 

 strand and groove ; b, labial lamina ; c, dental lamina ; d, enamel organ ; 



e, dental papilla. 



(4) Study a stained axial section of an infant's tooth some time 

 before eruption. Note: a, enamel organ (enamel, inner enamel epithe- 

 lium, outer enamel epithelium, and enamel pulp) ; b, dental pulp, odon- 

 toblasts and the strata of older and younger dentin; c, the dental sac; 

 d, anlage of the permanent tooth; e, remnant of the dental lamina. 

 Make l.p. sketch (231). Sketch h.p. (232) a small area near the apex 

 of the crown, showing from without inward : a, enamel pulp ; b, layer of 

 ameloblasts; c, Tomes' processes; d, enamel; e, membrana perf ormativa ; 



f, stratum of older basophilic dentin; g, stratum of younger acidophilic 

 (only slightly calcified) dentin with Tomes' fibrils; h, layer of odonto- 

 blasts ; i, dental pulp. 



(C.) THE TONGUE (Lingua). 



(1) Make diagram l.p. (233) of transverse section of a cat's tongue 

 to show the disposition of the striped muscle. Note the bilaterally sym- 

 metrical structure of the tongue; the extent of the medial septum lin- 

 guae; the difference between the mucous covering on the dorsum and 

 ventrum of the tongue. Note also the superficial longitudinal muscles, 

 the genio-glossus ventrally, and the deep transverse and vertical fibers. 

 Note further the glands imbedded in the muscle. 



(2) Sketch from stained sections of the human tongue the several 



