76 JOHN WABREN 



cially in the older stages, as a considerable amount of research 

 has aheady been devoted to their study and description. 



Part I. In Part I the development of the pineal region in 

 sheep embryos wall be considered, as these embryos in practically 

 every case studied from 21 mm. up to 48 mm. possess a dis- 

 tinct paraphysis and differ in this respect from all other mam- 

 mahan embryos that were available for study in the Harvard 

 Collection. 



Part II. In Part II the development of certain special features 

 only of the pineal region in human embryos will be discussed. 

 These are the formation of the primary arches, which can be 

 readily demonstrated in early human embryos; the formation 

 of the paraphysis, which can be seen in a few specimens only as 

 a very inconstant and a relatively rudimentary structure as 

 compared with that of vertebrates below the mammalia; finally 

 attention will be called particularly to a pecuUar set of tubular 

 outgrowths springing from the velar end of the postvelar arch 

 and overhanging the paraphysal arch and the paraphysis when 

 present. These will be referred to as the postvelar tubules or 

 diverticula 



Part III. Part III will contain a brief review of the develop- 

 ment of the forebrain roof in embryos of the opossum, rat, 

 rabbit, cow, pig, deer, cat and dog. Wax models on a scale of 

 40 diameters have been made to demonstrate the whole of the 

 forebrain in sheep embryos from 9 mm. up to 48 mm. and addi- 

 tional models on a scale of 100 diameters to show the details 

 of the paraphysis only in embryos of 28 mm. and 48 mm. Two 

 drawings on the same scale are added to point out the histo- 

 logical structure of the organ in those two specimens. To illus- 

 trate the development in human embryos models were recon- 

 structed of the whole forebrain at a magnification of 40 diameters 

 of embryos of 15 mm., 16 mm., and 23 mm. Other models 

 have also been reconstructed on a scale of 80 diameters of the 

 paraphysal arch, velum and oral or velar end of the postvelar 

 arch only and are intended to demonstrate details of the para- 

 physis and of the velar end of the diencephalic roof. The 

 figures of the wax models are in all cases reduced to one-half 

 the linear dimensions of the wax models themselves. 



