496 Dr. F. W. Mott and Miss A. M. Kelley. [ Mar. 6, 
sulcus rectus, the anterior end of the sulcus lateralis, and the intercalary 
sulcus (vide fig. 1).  Posteriorly and anteriorly this type becomes less 
characteristic, and gradually merges, in front, into an area intermediate 
to the motor and the frontal types; and behind, into one intermediate to the 
motor and the precentral type. This lamination is continued further 
forward within the sulcus rectus than can be indicated on the surface 
diagram. 
Motor B FE] —Type “Motor B” covers the space which les between 
the extremities of the sulcus rectus and the sulcus lateralis, and extending 
downwards on to the superior wall of the Sylvian fissure is bounded 
inferiorly by the sulcus which lies at its base. (A more particular description 
of this sulcus is given under “Type R.”) Superiorly it merges into 
“Motor A,” anteriorly into an area intermediate to this type and type 
“Frontal B,”’ and posteriorly into one intermediate to this type and the 
temporal and post-central types. 
Characteristics : Motor A. The cortex is about 2 mm. deep—the molecular 
layer measuring about 0°17 mm., the pyramidal layer and granules together 
about 0°9 mm., the pallid zone in which the Betz cells lie about 0:2 mm., 
and the polymorph layer about 0°7 mm. (vide fig. 5, Plate 14). The cells of 
the pyramidal layer are larger and have more processes than in other parts 
of the cortex (those of the post-central and temporal types most nearly 
approaching them in form). They are somewhat irregularly arranged, owing 
perhaps to the presence of the fibres from the Betz cells. Granules are 
scattered in fair numbers at the bottom of the pyramidal layer; but they do 
not form a distinct layer. The infra-granular pyramids are the most typical 
features of this area. They are for the most part well-formed Betz cells, 
containing Nissl bodies and having several branched processes. They 
frequently measure as much as 60 w by 25 w, and are sometimes larger. This 
line of cells seems to occupy a pallid zone in which only a few other cells 
are scattered—these being smaller Betz-like cells, faintly-stained pyramidal 
cells, and a few granules. Some of the large Betz cells closely resemble the 
typical giant Betz cells of the cortex of the higher apes, but many are more 
pyramidal in shape. The tendency to arrangement in nests which has been 
described in the human cortex is not general, though it can sometimes 
be seen. The largest Betz cells are found immediately before and behind 
the small fissuret which lies in the middle of this area, and between it and 
the intercalary sulcus. 
Motor B (vide fig. 6)—In “Motor B” the pyramidal cells are smaller 
than in “Motor A”; a line of darkly staining stellate cells is scattered 
