EXPLANATION OF FIGURES 



All figures are from preparations of embryos of the cat, the lengths of which 

 are indicated. With the exception of figures 17 and 18, the drawings are the 

 work of Mr. C. D. Jarrett. 



In the model from which figures 1 to 5, 12, 13 have been made, cartilaginous 

 parts only are represented on the left side; on the right side, in addition, are 

 shown vessels, nerves and bones. In figures 1 and 2, the right otic capsule is 

 represented as partly opened. In figure 3, the incudal cartilage and part of 

 Meckel's cartilage have been omitted. Figures 15 to 30 are camera lucida draw- 

 ings of the sections represented. Figures 19 to 30 are from sections of the 23.1 

 mm. embryo (H. E. C. Series 466); the number of the section is indicated in 

 each fieure. 



Fig. 1 From a model of the cranium of an embryo 23.1 mm. long (H. E. C. 

 Series 466) Dorsal aspect, X -/. 



Fig. 2 The same; ventral aspect. 



Fig. 3 The same; left lateral aspect. 



Fig. 4 The same; right lateral aspect. 



Fig. 5 From a van Wijhe preparation of the head of an embryo 10.5 mm. 

 long (W. A. C. No. 310). Dorsal aspect, X V- 



Fig 6 From a van Wijhe preparation of the head of an embryo 12 mm. long 

 (W. A. C. No. 311). Left side and base seen froni the right, X r. 



Fig. 7 From a van Wijhe preparation of the head of an embryo 15 mm. long 

 (W. A. C. No. 312). Dorsal aspect, X V. The breadth of this is somewhat 

 exaggerated, the ala temporalis being too far toward the side. 



Fig. 8 From van Wijhe preparations of the heads of embryos 18-20 mm. 

 long (W. A. C. Nos. 313, 314). Dorsal aspect, X V. 



Fig. 9 From a van Wijhe preparation of the head of an embryo 24 mm. long 

 (W. A. C. No. 315). Right occipital and otic regions seen from the left. In 

 this, as in all the van Wijhe preparations, the cochlear capsule is for the most 

 part only lightly stained. X V^. 



Fig. 10 From a model of the left otic capsule, of an embryo 23.1 mm. long 

 (H. E. C. Series 466). The large, cut surface is in a frontal plane through the 

 middle of the vestibule. Dorsal and medial aspect, X t". 



Fig. 11 The same as figure 10, excepting the level of the cut surface, which 

 is at the ventral part of the vestibule. 



Fig. 12 Region of the foramen rotundum as it appears in the model of the 

 23.1 mm. embryo. Ventral and caudal aspect, X t". 



Fig. 13 Ethmoidal skeleton; from the model of the 23.1 mm. embryo. Rep- 

 resents the left half from its medial aspect, the septal cartilage being omitted 

 and the nasal tectum, laminae transversales and lamina infracribrosa sectioned 

 just to the left of and parallel with the median plane. X -Y' 



Fig. 14 From a model of the basal plate and epistropheus in median section 

 showing the course of the notochord. Embryo 23.1 mm. long. X ¥. 



Fig. 15 Transverse section through the occipital region. Embryo 10.6 mm. 

 long (H. E. C. Series 476, sect. 300). X V'- 



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