THE CONNECTIVE TISSUES AND THE SKELETAL SYSTEM. 219 



celloidin, stained with Weigert's haematoxylin and eosin and mounted in xylol-damar 

 (see Appendix). 



Ossification of the vault of the skull can be studied in pig embryos of 40 mm. and longer 

 by means of the technic described under Intramembranous Bone (p. 218). 



Ossification of the appendicular skeleton can be studied in the extremities of pig embryos 

 of three inches and longer, by means of the technic for Intracartilaginous Bone (p. 218). 



Models of parts or of the whole of the osseous skeleton can be made by the method of 

 plastic reconstruction. For this, of course, serial sections are necessary (see Appendix). 



Transparent Preparations. A method which renders the tissues more or less transparent 

 and differentiates the bone is extremely useful in studying the development of the osseous 

 skeleton. Embryos of any kind are put into strong alcohol and left indefinitely the longer 

 the better. They become much shrunken, but that is not injurious. They are then put into 

 a 3 per cent, aqueous solution of potassium hydrate (KOH). If the solution becomes colored 

 by the pigment from the blood it should be changed as often as necessary. The embryos 

 become quite transparent in a short time, a few days or more, depending upon their size. 

 They are then put carefully into equal parts of glycerin and water for a day or two, then into 

 stronger glycerin, and finally preserved in pure glycerin. The tissues, except bone, are 

 quite transparent; the bone remains white, and the entire osseous skeletal system, so far as 

 it is developed at any particular stage, can be seen clearly. 



For technic to demonstrate the growth of bones, see small print in the text, page 180. 



Fat. Fix bits of tissue from the axilla and groin of a five- or six-inch fcetal pig in i per 

 cent, osmic acid for twenty-four hours. Wash in running water for several hours and 

 preserve in pure glycerin. Tease small pieces of tissue on a slide and mount in glycerin. 



References for Further Study. 



ADOLPHI, H. : Ueber die Variationen des Brustkorbes und der Wirbelsaule des Menschen. 

 Morph. Jahrbuch, Bd. XXIII, 1905. 



BADE, P.: Die Entwickelung des menschlichen Skeletts bis zur Geburt. Arch. f. mik. 

 Anat., Bd. LV, 1900. 



BARDEEN, C. R.: Numerical Vertebral Variations in the Human Adult and Embryo. 

 Anat. Anz., Bd. XXV, 1904. 



BARDEEN, C. R.: Studies of the Development of the Human Skeleton. American 

 Jour, of Anat., Vol. IV, 1905. 



BARDEEN, C. R.: The Development of the Thoracic Vertebrae in Man. American 

 Jour, of Anat., Vol. IV, 1905. 



BARTELS, M.: Ueber Menschenschwanze. Arch. f. Anthropol, Bd. XII. 



BERNAYS, A.: Die Entwickelungsgeschichte des Kniegelenkes des Menschen mit 

 Bemerkungen liber die Gelenke im allgemeinen. Morph. Jahrbuch, Bd. IV, 1878. 



BOLL, F.: Die Entwickelung des fibrillaren Bindegewebes, Arch. f. mik. Anat., Bd. 

 VIII, 1872. 



BOLK, L.: Beziehungen zwischen Skelett, Muskulatur und Nerven der Extremitaten, 

 etc. Morph. Jahrbuch, Bd. XXI, 1894. 



BONNET, R.: Lehrbuch der Entwickelungsgeschichte. Berlin, 1907. 



BRAUS, H.: Die Entwickelung der Form der Extremitaten und des Extremitatenskeletts. 

 In Hertwig's Handbuch der vergleich. u. experiment. Entwickelungslehre der Wirbeltiere, Bd 

 III, Teil II, 1904. 



FAWCETT, E. : On the Early Stages in the Ossification of the Pterygoid Plates of the 

 Sphenoid Bone of Man. Anat. Anz., Bd. XXVI, 1905. 



